Staff

Abstract:
A new detailed dataset of breast ultrasound scans (BrEaST) containing images of benign and malignant lesions as well as normal tissue examples, is presented. The dataset consists of 256 breast scans collected from 256 patients. Each scan was manually annotated and labeled by a radiologist experienced in breast ultrasound examination. In particular, each tumor was identified in the image using a freehand annotation and labeled according to BIRADS features and lexicon. The histopathological classification of the tumor was also provided for patients who underwent a biopsy.
The BrEaST dataset is the first breast ultrasound dataset containing patient-level labels, image-level annotations, and tumor-level labels with all cases confirmed by follow-up care or core needle biopsy result. To enable research into breast disease detection, tumor segmentation and classification, the BrEaST dataset is made publicly available with the CC-BY 4.0 license.

Abstract:
Fast and high-quality ultrasound imaging allows to increase the effectiveness of detecting tissue changes at the initial stage of disease. The aim of the study was to assess the quality of ultrasound imaging using mutually
orthogonal, complementary Golay coded sequences (MOCGCS). Two 16-bits MOCGCS sets were implemented in the Verasonics Vantage™ scanner. Echoes from a perfect reflector, a custom-made nylon wire phantom,a tissue-mimicking phantom, and in-vivo scans of abdominal aorta and common carotid artery were recorded.Three parameters of the detected MOCGCS echoes: signal-to-noise ratio (SNR), side-lobe level (SLL), and axial resolution were evaluated and compared to the same parameters of the echoes recorded using standard
complementary Golay sequences (CGS) and a short, one sine cycle pulse. The results revealed that MOCGCS
transmission maintained comparable echo quality metrics (SNR, SLL, and axial resolution) compared to CGS
and short pulses. Notably, both MOCGCS and CGS offered similar SNR improvements (5 dB–9 dB) in compar-ison to the short pulse for wires placed at depths up to 8 cm. Analysis of axial resolution, estimated at the full width at half maximum level, revealed near-identical values for all transmitted signals (0.17 μs for MOCGCS,0.16 μs for CGS, and 0.18 μs for short pulse). MOCGCS implementation in ultrasound imaging offers the po-tential to significantly reduce image reconstruction time while maintaining image quality comparable to CGS sequences. In the experimental study we have shown that MOCGCS offers advantages over conventional CGS by enabling two times faster data acquisition and image reconstruction without compromising image quality.

Keywords:
coded excitation, Golay codes, synthetic aperture

Abstract:
Janusz Wójcik was born in the heart of Poland near Czarnolas in August 1957. He obtained an M.Sc. Eng. degree at the Warsaw University of Technology in 1983. From 1984 until the last days of his life, he worked at the Institute of Fundamental Technological Research Polish Academy of Sciences in Warsaw. He received his doctoral degree on the basis of the dissertation “Nonlinear EnvelopeWaves in The Vlasov-Maxwell Plasma” in 1990. In 2004, he was given a permanent position of IPPT PAN professor and a year later he was appointed Head of the Ultrasound Introscopy Laboratory at the Department of Ultrasound.

Keywords:
Janusz Wójcik

Abstract:
In our research we present a new method of differential compression of the Golay encoded ultrasound (DCGEU) in the standard beamforming mode to visualize the slow (<1cm/s) blood mimicking fluid flow in small diameter tubes. The proposed DCGEU method is based on synthesis of several subsequent B-mode frames acquired with certain time intervals (30 ms in this study) followed by the visualization of differential beamformed radio frequency (RF) echoes, which yielded the images of the scatterers moving slowly in the vessel and suppressing the static echoes outside the vessel. In order to extract small backscattered echoes from the vessel area we took an advantage of improved sensitivity of the complementary Golay coded sequences (CGCS).
The validation of the proposed DCGEU method was carried out in two stages. In the first one, we compared the flow images in small tubes with a diameter of 1 mm and 2.5 mm, reconstructed from numerically simulated acoustic data for the standard transmission of short pulses and 16-bits long CGCS signals. In the second stage of the research, the experimental data were acquired in a flow phantom with silicone tubes with an internal diameter of 1.5 mm and 4.5 mm and a fluid flow velocity of 0.9 cm/s. The experiments were carried out using preprogrammed Verasonics Vantage™ research ultrasound system equipped with ALT L12-5/50 mm MHz linear array transducer with 7.8 MHz center frequency.
It was evidenced both in simulations and experiments that the DCGEU provided a good flow image along the entire length of tubing with virtually angle independent detection in comparison with the conventional short pulse interrogation.

Keywords:
Coded excitation; Flow imaging; Ultrasound imaging; Classical beamforming

Abstract:
In this paper, we propose a novel deep learning method for joint classification and segmentation of breast masses based on radio-frequency (RF) ultrasound (US) data. In comparison to commonly used classification and segmentation techniques, utilizing B-mode US images, we train the network with RF data (data before envelope detection and dynamic compression), which are considered to include more information on tissue’s physical properties than standard B-mode US images. Our multi-task network, based on the Y-Net architecture, can effectively process large matrices of RF data by mixing 1D and 2D convolutional filters. We use data collected from 273 breast masses to compare the performance of networks trained with RF data and US images. The multi-task model developed based on the RF data achieved good classification performance, with area under the receiver operating characteristic curve (AUC) of 0.90. The network based on the US images achieved AUC of 0.87. In the case of the segmentation, we obtained mean Dice scores of 0.64 and 0.60 for the approaches utilizing US images and RF data, respectively. Moreover, the interpretability of the networks was studied using class activation mapping technique and by filter weights visualizations.

Keywords:
breast mass classification, breast mass segmentation, convolutional neural networks, deep learning, quantitative ultrasound, ultrasound imagin

Abstract:
Kidney Cooling Jacket (KCJ) preserves the kidney graft, wrapped in the jacket, against the too fast time of temperature rise during the operation of connecting a cooled transplant to the patient’s bloodstream. The efficiency of KCJ depends on the stationarity of the fluid flow and its spatial uniformity. In this paper, the fluid velocity field inside the three different KCJ prototypes has been measured using the 20 MHz ultrasonic Doppler flowmeter. The simplified 2D geometrical model of the prototypes has been presented using COMSOL-Multiphysics to simulate the fluid flow assuming the laminar flow model. By comparing the numerical results with experimental data, the simplified 2D model is shown to be accurate enough to predict the flow distribution of the internal fluid velocity field within the KCJ. The discrepancy between the average velocity measured using the 20 MHz Doppler and numerical results was mainly related to the sensitivity of the velocity measurements to a change of the direction of the local fluid flow stream. Flux direction and average velocity were additionally confirmed by using ommercial colour Doppler imaging scanner. The current approach showed nearly 90% agreement of the experimental results and numerical simulations. It was important for justifying the use of numerical modelling in designing the baffles distribution (internal walls in the flow space) for obtaining the
most spatially uniform field of flow velocity.

Keywords:
multi-canal system; fluid flow prediction; cooling jacket; flow Doppler measurement

Abstract:
Background. Blood flow-mediated dilation (FMD) is a noninvasive assessment of vascular endothelial function in humans. The study of the FMD in hypertensive (HT) patients is an important factor supporting the recognition of the early mechanisms of cardiovascular pathologies, and also of the pathogenesis related to hypertension. Objectives. To investigate whether FMD measured on the radial artery (FMD-RA) using high-requency ultrasounds can be used asan alternative to FMD assessed with the lower frequency system onthe brachial artery in patients with HT. Materials and methods. The simultaneous measurements of FMD-RA and FMD measurements in the brachial artery (FMD-BA) were performed on 76 HT patients using 20 MHz and 7–12 MHz linear array probes, and were compared to the FMD measured in healthy groups. All quantitative data are presented as mean ± standard deviation (SD); the p-values of the normality and tests for variables comparisons are listed. The agreement of the FMD-RA and FMD-BA in HT patients was assessed with the Bland–Altman method, and using the intraclass correlation coefficient (ICC). In some statistical calculations, the FMD-RA values were rescaled by dividing them by a factor of 2. Results. The mean FMD-RA and FMD-BA in HT patients were 5.16 ±2.18% (95% confidence interval (95% CI): [4.50%, 5.82%]) and 2.13 ±1.12% (95% CI: [1.76%, 2.49%]), respectively. The FMD-RA and FMD-BA values of HT patients were significantly different than those in respective control groups. The p-values of Mann–Whitney–Wilcoxon tests were less than 0.05. The Bland–Altman coefficient for both measurement methods, FMD-RA and FMD-BA, was 3%, and the ICC was 0.69. Conclusions. Our findings show that FMD-RA, supplementary to FMD-BA measurements, can be used to assess endothelial dysfunction in the group of HT patients. In addition, the FMD-RA measurements met the criteria of high concordance with the FMD-BA measurements.

Keywords:
hypertension, brachial artery, radial artery, endothelial function

Abstract:
Complementary Golay coded sequences (CGCS) have several advantages over conventional short pulse trans-mitted signals. Specifically, CGCS allow the signal-to-noise ratio (SNR) to be increased. Moreover, due to matched filtering and compression, echoes resembling the short pulse waveform with substantially higher amplitude can be obtained. However, CGCS require two subsequent transmissions to obtain a single compressed signal. This decreases the data acquisition rate and the frame rate of ultrasound imaging by two-fold. To alleviate this problem, mutually orthogonal Golay complementary sequences (MOGCS) can be used. MOGCS allow the simultaneous transmission of two CGCS pairs to be implemented, yielding the acoustic data for two image frames in one data acquisition cycle. The main objective of this work was an experimental study of the most crucial parameters of the received acoustic signals, e.g. the signal-to-noise ratio (SNR), the side-lobes level (SLL) of the signal and the axial reso-lution, obtained from simultaneous transmission of two pairs of CGCS comprising a MOGCS set to demonstrate their feasibility of being used in ultrasonography. For this purpose, a simultaneous synthetic transmit aperturę method (SSTA) was proposed. The SSTA is based on MOGCS transmission and simultaneous reconstruction of two image frames from a single data acquisition cycle. This doubles the image reconstruction rate in comparison with conventional CGCS signals. In this paper, the ultrasound data from a perfect reflector, commercial phantoms and in vivo measurements were analysed. Two 16-bit long CGCS pairs comprising the MOGCS set were programmed and transmitted using the Verasonics Vantage™ research ultrasound system equipped with a Philips ATL L7-4 linear array ultrasound probe. It was shown that the signal parameters and overall quality of reconstructed B-mode images did not deteriorate when using the MOGCS in comparison to the conventional CGCS and short pulse signals explored so far.

Keywords:
coded excitation, mutually orthogonal, Golay codes, synthetic aperture, ultrasound imaging

Abstract:
The brain is subject to damage, due to ageing, physiological processes and/or disease. Some of the damage is acute in nature, such as strokes; some is more subtle, like white matter lesions. White matter lesions or hyperintensities (WMH) can be one of the first signs of micro brain damage. We implemented the Acoustocerebrography (ACG) as an easy to use method designed to capture differing states of human brain tissue and the respective changes. Aim: The purpose of the study is to compare the efficacy of ACG and Magnetic Resonance Imaging (MRI) to detect WMH in patients with clinically silent atrial fibrillation (AF). Methods and results: The study included 97 patients (age 66.26 ± 6.54 years) with AF. CHA2DS2- VASc score (2.5 ±1.3) and HAS BLED (1.65 ± 0.9). According to MRI data, the patients were assigned into four groups depending on the number of lesions: L0 – 0 to 4 lesions, L5 – 5 to 9 lesions, L10 – 10 to 29 lesions, and L30 – 30 or more lesions. Authors found that the ACG method clearly differentiates the groups L0 (with 0–4 lesions) and L30 (with more than 30 lesions) of WMH patients. Fisher's Exact Test shows that this correlation is highly significant (p < 0.001). Conclusion: ACG is a new, easy and cost-effective method for detecting WMH in patients with atrial fibrillation. The ACG measurement methodology should become increasingly useful for the assessment of WMH.

Keywords:
acoustocerebrography, brain MRI, atrial fibrillation, white matter hyperintensities

Abstract:
The article presents a new normalization of flow-mediated dilation (FMD) in the radial artery, taking into account the parameter BSSR being equal to the ratio of the basal shear rate (BS) measured before the cuff inflation and post occlusive shear rate (SR). The in vivo usefulness of the new normalization algorithm wasevaluated in two groups of patients. In group I, comprising 15 healthy volunteers, the normalized FMD/SR was(3.19 ± 1.4)*10^-4, while in group II, comprising 13 patients with stable coronary artery disease (CAD), it was(1.02 ± 0.76)*10^-4. We calculated almost 50% larger difference between the average values after normalizing FMD/BSSR. Specifically, the FMD/BSSR was equal to 28 ± 9.40 in group I and 6.01 ± 3.74 in group II. The prediction of CAD patients based on FMD/SR values had a sensitivity of 83.3% and a specificity of 84.6%, whereas the prediction of CAD patients based on the FMD/BSSR values revealed 100% sensitivity and specificity. These results confirm the usefulness of the novel normalization algorithm of the FMD in differentiation of normal patients from those with stable CAD.

Keywords:
flow-mediated vasodilation, radial artery, shear rate, pulsed Doppler, ultrasonography, coronary artery disease

Abstract:
This review article combines the reports on the biophysical effects in ultrasonography and provides the rationale behind the mechanical index (MI) and thermal index (TI) complying with the Output Display Standard (ODS). Safe ultrasonic doses are determined according to specific rules, and the screen displays the associated quantities MI and TI. The introduced indices MI and TI take into account the physical mechanism of interaction between ultrasounds and biological tissue, which depends on the temporal and spatial parameters of the acoustic field generated by ultrasound transducers. The predicted temperature increase is determined using three different tissue models: homogeneous, layered and bone/tissue interface.

Keywords:
ultrasonography, thermal index, mechanical index, cavitation, international electrotechnical commission standards

Abstract:
In the article we describe the new, high frequency, 20 MHz scanning/Doppler probe designed to measure the flow mediated dilation (FMD) and shear rate (SR) close to the radial artery wall. We compare two US scanning systems, standard vascular modality working below 12 MHz and high frequency 20 MHz system designed for FMD and SR measurements. Axial resolutions of both systems were compared by imaging of two closely spaced food plastic foils immersed in water and by measuring systolic/diastolic diameter changes in the radial artery. The sensitivities of Doppler modalities were also determined. The diagnostic potential of a high frequency system in measurements of FMD and SR was studied in vivo, in two groups of subjects, 12 healthy volunteers and 14 patients with stable coronary artery disease (CAD). Over three times better axial resolution was demonstrated for a high frequency system. Also, the sensitivity of the external single transducer 20 MHz pulse Doppler proved to be over 20 dB better (in terms of a signal-to-noise ratio) than the pulse Doppler incorporated into the linear array. Statistically significant differences in FMD and FMD/SR values for healthy volunteers and CAD patients were confirmed, p-values < 0:05. The areas under Receiver Operating Characteristic (ROC) curves for FMD and FMD/SR for the prediction CAD had the values of 0.99 and 0.97, respectively. These results justify the usefulness of the designed high-frequency scanning system to determine the FMD and SR in the radial artery as predictors of coronary arterial disease.

Keywords:
low mediated dilation, shear rate, axial resolution, elevation resolution, pulsed Doppler, ultrasonic imaging

Abstract:
W ciągu ostatnich kilku dziesięcioleci ultradźwięki znalazły szerokie zastosowanie w diagnostyce obrazowej. Ten artykuł przeglądowy omawia potencjalne efekty biologiczne związane z propagacją ultradźwięków w tkankach i podaje fizyczne podstawy wprowadzonych indeksów mechanicznego MI i ter micznego TI zgodnych z Output Display Standard (ODS). W praktyce klinicznej otrzymywane wyniki są kompromisem pomiędzy jakością obrazu a możliwością systemu uzyskiwania zadowalających obrazów głęboko leżących struktur tkankowych – wyboru dokonuje się, biorąc pod uwagę minimalizację bioefektów. Moce wyjściowe ultrasonografów są regulowane i ograniczane do określonych poziomów. Bezpieczne dawki ultradźwiękowe wyznacza się według określonych zasad, a na ekranie wyświetlane są związane z nimi wielkości. Wielkości te określają możliwości wystąpienia zmian mechanicznych i termicznych w tkankach i dlatego mają znaczenia kliniczne. Wprowadzone wskaźniki – mechaniczny MI i termiczny TI uwzględniają fizyczny mechanizm oddziaływania między ultradźwiękami i biologiczną tkanką, który zależy od czasowych i przestrzennych parametrów pola akustycznego generowanego przez głowice ultradźwiękowe. Przewidywany wzrost temperatury określa się, stosując trzy różne modele tkankowe: homogeniczny, warstwowy i układ kość/tkanka.
Ultrasounds have found widespread use in imaging diagnostics over the past few decades. This review article combines the reports on the biophysical effects and provides the rationale behind the mechanical index (MI) and thermal index TI complying with Output Display Standard (ODS). In clinical practice, the obtained diagnostic results are a compromise between the quality of the image and the possibility of a system of obtaining satisfactory images of deep-lying tissue structures – the choice is made taking into account the minimization of bioeffects. The output powers of ultrasonographs are regulated and limited to specific levels. Safe ultrasonic doses are determined according to specific rules, and the screen displays the associated quantities. These quantities determine the possibility of mechanical and thermal changes in the tissues and therefore have clinical significance. The introduced indexes MI and TI take into account the physical mechanism of interaction between ultrasounds and biological tissue, which depends on the temporal and spatial parameters of the acoustic field generated by ultrasound transducers. The predicted temperature increase is determined using three different tissue models: homogeneous, layered and bone/tissue interface.

Keywords:
ultrasonografia, wskaźnik termiczny TI, wskaźnik mechaniczny MI, kawitacja, standardy IEC / ultrasonography, thermal index TI, mechanical index MI, cavitation, IEC standards

Abstract:
Acoustocerebrography is a novel, non-invasive, transcranial ultrasonic diagnostic method based on the transmission of multispectral ultrasound signals propagating through the brain tissue. Dedicated signal processing enables the estimation of absorption coefficient, frequency-dependent attenuation, speed of sound and tissue elasticity. Hypertension and atrial fibrillation are well known factors correlated with white matter lesions, intracerebral hemorrhage and cryptogenic stroke numbers. The aim of this study was to compare the acoustocerebrography signal in the brains of asymptomatic atrial fibrillation patients with and without hypertension. The study included 97 asymptomatic patients (40 female and 57 male, age 66.26 +/- 6.54 years) who were clinically monitored for atrial fibrillation. The patients were divided into two groups: group I (patients with hypertension) n = 75, and group II (patients without hypertension) n = 22. Phase and amplitude of all spectral components for the received signals from the brain path were extracted and compared to the phase and amplitude of the transmitted pulse. Next, the time of flight and the attenuation of each frequency component were calculated. Additionally, a fast Fourier transformation was performed and its features were extracted. After introducing a machine learning technique, the ROC plot of differentiations between group I and group II with an AUC of 0.958 (sensitivity 0.99 and specificity 0.968) was obtained. It can be assumed that the significant difference in the acoustocerebrography signals in patients with hypertension is due to changes in the brain tissue, and it allows for the differentiating of high-risk patients with asymptomatic atrial fibrillation and hypertension.

Keywords:
changes in the brain, hypertension in atrial, acoustocerebrography

Abstract:
A high-frequency scanning system consisting of a 20-MHz linear array transducer combined with a 20-MHz pulsed Dopplerprobe was introduced to evaluate the degree of radial artery flow-mediated dilation (FMD [%]) in two groups of patients after5 min of controlled forearm ischemia followed by reactive hyperemia. In group I, comprising 27 healthy volunteers, FMD (mean ± standard deviation) was 15.26 ± 4.90% (95% confidence interval [CI]: 13.32%–17.20%); in group II, comprising 17 patients with chronic coronary artery disease, FMD was significantly less at 4.53 ± 4.11% (95% CI: 2.42%–6.64%). Specifically, the ratio FMD/SR (mean ± standard deviation),wasequalto5.36×10−4±4.64×10−4 (95%CI:3.54×10−4 to7.18×10−4)ingroupIand1.38×10−4±0.89×10−4 (95% CI: 0.70 × 10−4 to 2.06 × 10−4) in group II. Statistically significant differences between the two groups were confirmed by a Wilcoxon–Mann–Whitney test for both FMD and FMD/SR (p < 0.01). Areas under receiver operating characteristic curves for FMD and FMD/SR were greater than 0.9. The results confirm the usefulness of the proposed measurements of radial artery FMD and SR in differentiation of normal patients from those with chronic coronary artery disease. (E-mail: ) © 2018 World Federation for Ultrasound in Medicine & Biology. All rights reserved.

Keywords:
Flow-mediated vasodilation, Radial artery, Shear rate, Reactive hyperemia, Endothelium, Pulsed doppler, Ultrasonography

Abstract:
This letter analyses the influence of the transducer bandwidth on the compression and the axial resolution of an ultrasound image. The distortion of an electrical signal visible in the final image is a major problem in ultrasonography. To solve this problem, the bit length in Golay-complementary sequences was elongated, narrowing the fractional bandwidth of the coded sequences. Therefore, more energy of the burst signal could be transferred through the ultrasound transducer. The experimental results obtained for transmission of the complementary Golaycoded sequences with two different bit lengths—one-cycle and two-cycles—have been compared, and the efficiency of the pulse compression and its influence on the axial resolution for two fractional bandwidths have been discussed. The results are presented for two transducers having a fractional bandwidth of 25% and 80% and operating at a 6-MHz frequency. The results obtained show that the elongation of the Golay single bit length (doubled in our case) compensate for the limited transducer bandwidth. Twodimensionalultrasoundimagesofatissue-mimickingphantomare presented and demonstrate the benefits of the use of two-cycle bit length.

Keywords:
Coded excitation, Golay sequences, synthetic aperture method, transducer bandwidth, ultrasound imaging

Abstract:
Purpose
The nonalcoholic fatty liver disease is the most common liver abnormality. Up to date, liver biopsy is the reference standard for direct liver steatosis quantification in hepatic tissue samples. In this paper we propose a neural network-based approach for nonalcoholic fatty liver disease assessment in ultrasound.
Methods
We used the Inception-ResNet-v2 deep convolutional neural network pre-trained on the ImageNet dataset to extract high-level features in liver B-mode ultrasound image sequences. The steatosis level of each liver was graded by wedge biopsy. The proposed approach was compared with the hepatorenal index technique and the gray-level co-occurrence matrix algorithm. After the feature extraction, we applied the support vector machine algorithm to classify images containing fatty liver. Based on liver biopsy, the fatty liver was defined to have more than 5% of hepatocytes with steatosis. Next, we used the features and the Lasso regression method to assess the steatosis level.
Results
The area under the receiver operating characteristics curve obtained using the proposed approach was equal to 0.977, being higher than the one obtained with the hepatorenal index method, 0.959, and much higher than in the case of the gray-level co-occurrence matrix algorithm, 0.893. For regression the Spearman correlation coefficients between the steatosis level and the proposed approach, the hepatorenal index and the gray-level co-occurrence matrix algorithm were equal to 0.78, 0.80 and 0.39, respectively.
Conclusions
The proposed approach may help the sonographers automatically diagnose the amount of fat in the liver. The presented approach is efficient and in comparison with other methods does not require the sonographers to select the region of interest.

Keywords:
Nonalcoholic fatty, liver disease, Ultrasound imaging Deep learning, Convolutional neural networks, Hepatorenal index, Transfer learning

Abstract:
Quantitative ultrasound has been widely used for tissue characterization. In this paper we propose a new approach for tissue compression assessment. The proposed method employs the relation between the tissue scatterers' local spatial distribution and the resulting frequency power spectrum of the backscat- tered ultrasonic signal. We show that due to spatial distribution of the scatterers, the power spectrum exhibits characteristic variations. These variations can be extracted using the empirical mode decomposition and analyzed. Validation of our approach is performed by simulations and in-vitro experiments using a tissue sample under compression. The scatterers in the compressed tissue sample approach each other and consequently, the power spectrum of the backscattered signal is modified. We present how to assess this phenomenon with our method. The proposed in this paper approach is general and may provide useful information on tissue scattering properties.

Keywords:
tissue characterization, tissue compression, quantitative ultrasound, empirical mode decomposition, signal anaysis

Abstract:
Purpose: The aim of this paper is to provide access to a database consisting of the raw radio-frequency ultrasonic echoes acquired from malignant and benign breast lesions. The database is freely available for study and signal analysis. Acquisition and validation methods: The ultrasonic radio-frequency echoes were recorded from breast focal lesions of patients of the Institute of Oncology in Warsaw. The data were collected between 11/2013 and 10/2015. Patients were examined by a radiologist with 18 yr' experience in the ultrasonic examination of breast lesions. The set of data includes scans from 52 malignant and 48 benign breast lesions recorded in a group of 78 women. For each lesion, two individual orthogonal scans from the pathological region were acquired with the Ultrasonix SonixTouch Research ultrasound scanner using the L14-5/38 linear array transducer. All malignant lesions were histologically assessed by core needle biopsy. In the case of benign lesions, part of them was histologically assessed and another part was observed over a 2-year period. Data format and usage notes: The radio-frequency echoes were stored in Matlab file format. For each scan, the region of interest was provided to correctly indicate the lesion area. Moreover, for each lesion, the BI-RADS category and the lesion class were included. Two code examples of data manipulation are presented. The data can be downloaded via the Zenodo repository (https://doi.org/10.5281/zenodo.545928) or the website http ://bluebox.ippt.gov.pl/~hpiotrzk. Potential applications: The database can be used to test quantitative ultrasound techniques and ultrasound image processing algorithms, or to develop computer-aided diagno sis systems.

Keywords:
breast lesions, dataset, ultrasonic signals, ultrasonography

Abstract:
The purpose of this work was to determine the influence of standing waves and possible multiple reflections under the conditions often encountered in examining the effects of ultrasound exposure on the cell cultures in vitro. More specifically, the goal was to quantitatively ascertain the influence of ultrasound exposure under free field (FF) and standing waves (SW) and multiple reflections (MR) conditions (SWMR) on the biological endpoint (50% cell necrosis). Such information would help in designing the experiments, in which the geometry of the container with biological tissue may prevent FF conditions to be established and in which the ultrasound generated temperature elevation is undesirable. This goal was accomplished by performing systematic, side-by-side experiments in vitro with C6 rat glioma cancer cells using 12 well and 96 well plates. It was determined that to obtain 50% of cell viability using the 12 well plates, the spatial average, temporal average (ISATA) intensities of 0.32 W/cm2 and 5.89 W/cm2 were needed under SWMR and FF conditions, respectively. For 96 well plates the results were 0.80 W/cm2 and 2.86 W/cm2 respectively. The corresponding, hydrophone measured pRMS maximum pressure amplitude values, were 0.71 MPa, 0.75 MPa, 0.75 MPa and 0.73 MPa, respectively. These results suggest that pRMS pressure amplitude was independent of the measurement set-up geometry and hence could be used to predict the cells' mortality threshold under any in vitro experimental conditions or even as a starting point for (pre-clinical) in vivo tests. The described procedure of the hydrophone measurements of the pRMS maximum pressure amplitude at the k/2 distance (here 0.75 mm) from the cell's level at the bottom of the dish or plate provides the guideline allowing the difference between the FF and SWMR conditions to be determined in any experimental setup. The outcome of the measurements also indicates that SWMR exposure might be useful at any ultrasound assisted therapy experiments as it permits to reduce thermal effects. Although the results presented are valid for the experimental conditions used in this study they can be generalized. The analysis developed provides methodology facilitating independent laboratories to determine their specific ultrasound exposure parameters for a given biological end-point under standing waves and multiple reflections conditions. The analysis also permits verification of the outcome of the experiments mimicking pre- and clinical environment between different, unaffiliated teams of researchers.

Keywords:
Standing wave, Ultrasound pressure, Ultrasound intensity, C6 glioma, Anticancer therapy, Sonodynamic therapy, Ultrasound bio-effects

Abstract:
A technique using pulsed High Intensity Focused Ultrasound (HIFU) to destroy deep-seated solid tumors is a promising noninvasive therapeutic approach. A main purpose of this study was to design and test a HIFU transducer suitable for preclinical studies of efficacy of tested, anti-cancer drugs, activated by HIFU beams, in the treatment of a variety of solid tumors implanted to various organs of small animals at the depth of the order of 1–2 cm under the skin. To allow focusing of the beam, generated by such transducer, within treated tissue at different depths, a spherical, 2-MHz, 29-mm diameter annular phased array transducer was designed and built. To prove its potential for preclinical studies on small animals, multiple thermal lesions were induced in a pork loin ex vivo by heating beams of the same: 6 W, or 12 W, or 18 W acoustic power and 25 mm, 30 mm, and 35 mm focal lengths. Time delay for each annulus was controlled electronically to provide beam focusing within tissue at the depths of 10 mm, 15 mm, and 20 mm. The exposure time required to induce local necrosis was determined at different depths using thermocouples. Location and extent of thermal lesions determined from numerical simulations were compared with those measured using ultrasound and magnetic resonance imaging techniques and verified by a digital caliper after cutting the tested tissue samples. Quantitative analysis of the results showed that the location and extent of necrotic lesions on the magnetic resonance images are consistent with those predicted numerically and measured by caliper. The edges of lesions were clearly outlined although on ultrasound images they were fuzzy. This allows to conclude that the use of the transducer designed offers an effective noninvasive tool not only to induce local necrotic lesions within treated tissue without damaging the surrounding tissue structures but also to test various chemotherapeutics activated by the HIFU beams in preclinical studies on small animals.

Keywords:
spherical annular phased array transducer, pulsed HIFU beam, electronically adjustable focal length, local tissue heating, thermal ablation, necrotic lesion

Abstract:
AIM: To develop a method combining the statistics of the ultrasound backscatter and the Breast Imaging-Reporting and Data System (BI-RADS) classification to enhance the differentiation of breast tumours. MATERIALS AND METHODS: The Nakagami shape parameter m was used to characterise the scatter properties of breast tumours. Raw data from the radiofrequency (RF) echo-signal and Bmode images from 107 (32 malignant and 75 benign) lesions and their surrounding tissue were recorded. Three different characteristic values of the shape parameters of m (maximum [mLmax], minimum [mLmin] and average [mLavg]) and differences between m parameters (Dmmax, Dmmin, Dmavg) of the lesions and their surrounding tissues were assessed. A lesion with a BI-RADS score of 3 was considered benign, while a lesion with a score of 4 was considered malignant (a cut-off of BI-RADS 3/4 was set for all patients). RESULTS: The area under the receiver operating characteristic (ROC) curve (AUC) was equal to 0.966 for BI-RADS, with 100% sensitivity and 54.67% specificity. All malignant lesions were diagnosed correctly, whereas 34 benign lesions were biopsied unnecessarily. In assessing the Nakagami statistics, the sum of the sensitivity and specificity was the best for mLavg (62.5% and 93.33%, respectively). Only four of 20 lesions were found over the cut-off value in BI-RADS of 4a. When comparing the differences in m parameters, Dmavg had the highest sensitivity of 90% (only three of 32 lesions were false negative). These three lesions were classified as BIRADS category 4c. The combined use of B-mode and mLmin parameter improve the AUC up to 0.978 (pĽ0.088), compared to BI-RADS alone.
CONCLUSION: The combination of the parametric imaging and the BI-RADS assessment does not significantly improve the differentiation of breast lesions, but it has the potential to better identify the group of patients with mainly benign lesions that have a low level of suspicion for malignancy with a BI-RADS score of 4a.

Abstract:
Temperature monitoring is essential for various medical treatments. In this work, we investigate the impact of temperature on backscattered ultrasound echo statistics during a high intensity focused ultrasound treatment. A tissue mimicking phantom was heated with a spherical ultrasonic transducer up to 56 _C in order to imitate tissue necrosis. During the heating, an imaging scanner was used to acquire backscattered echoes from the heated region. These data was then modeled with the homodyned K distribution. We found that the best temperature indicator can be obtained by combining two parameters of the model, namely the backscattered echo mean intensity and the effective number of scatterers per resolution cell. Next, ultrasonic thermometer was designed and used to create a map of the temperature induced within the tissue phantom during the treatment

Keywords:
Temperature monitoring, homodyned K distribution, focused ultrasound

Abstract:
Ultrasonic elastography is a technique allowing imaging of the elastic properties of tissue. There are two basic techniques of elastographic imaging; compressional - displaying the evaluation of tissue deformation under the external stress; and dynamic, tracking the propagation velocity of the shear wave generated by the acoustic radiation force. Soft tissue bulk modulus varies, from a few to several GPa, whereas the shear modulus is significantly smaller, not exceeding a few hundred Pa for adipose tissue, breast or liver, up to several hundred kPa for hard tissue. Forces generated in the tissue due to the external, axial piston-like stresses depend mainly on the shear modulus. In Shear Wave Elastography, long, several tens of microseconds, ultrasonic pulses successively focused at several depths are sent: generating a conical wave front moving with the supersonic velocity, depending on the tissue stiffness. Velocity of propagation of shear wave depends on the shear modulus μ and the modulus of elasticity E of the examined tissue is equal to E=3μ.

Keywords:
elastography, ultrasonic imaging, thyroid, breast

Abstract:
Streaming velocity depends on intensity and absorption of ultrasound in the media. In some cases, such as ultrasound scattered on blood cells at high frequencies, or the presence of ultrasound contrast agents, scattering affects the streaming speed. The velocities of acoustic streaming in a blood-mimicking starch suspension in water and Bracco BR14 contrast agent were measured. The source of the streaming was a plane 20MHz ultrasonic transducer. Velocity was estimated from the averaged Doppler spectrum. The single particle driving force was calculated as the integral of the momentum density tensor components. For different starch concentrations, the streaming velocity increased from 8.9 to 12.5mm/s. This corresponds to a constant 14% velocity increase for a 1 g/l increase in starch concentration. For BR14, the streaming velocity remained constant at 7.2mm/s and was independent of the microbubbles concentration. The velocity was less than in reference, within 0.5mm/s measurement error. Theoretical calculations showed a 16% increase in streaming velocity for 1 g/l starch concentration rise, very similar to the experimental results. The theory has also shown the ability to reduce the streaming velocity by low-density scatterers, as was experimentally proved using the BR14 contrast agent.

Keywords:
ultrasound, radiation force, starch, contrast agent, blood, thrombolysis

Abstract:
Purpose:
Statistical modeling of an ultrasound backscattered echo envelope is used for tissue characterization. However, in the presence of complex structures within the analyzed area, estimation of parameters is disturbed and unreliable, e.g., in the case of breast tumor classification. In order to improve the differentiation of breast lesions, the authors proposed a method based on the segmentation of homodyned K distribution parameter maps. Regions within lesions of different scattering properties were extracted and analyzed. In order to improve the classification, the best-performing features were selected from various regions and then combined.

Methods:
A radio-frequency data set consisting of 103 breast lesions was used in the authors’ analysis. Maps of homodyned K distribution parameters were created using an algorithm based on signal-to-noise ratio, kurtosis, and skewness of fractional-order envelope moments. A Markov random field model was used to segment parametric maps. Features of different segments were extracted and evaluated based on bootstrapping and the receiver operating characteristic curve. To determine the best-performing feature subset, the authors applied the joint mutual information criterion.

Results:
It was found that there were individual features which performed better than the ones commonly used for lesion characterization, like the parameter obtained through averaging of values over the whole lesion. The authors selected and discussed the best-performing features. Properties of different extracted regions were important and improved the distinction between benign and malignant tumors. The best performance was obtained by combining four features with the area under the receiver operating curve of 0.84.

Conclusions:
The study showed that the analysis of internal changes in lesion parametric maps leads to a better classification of breast tumors. The authors recommend combining multiple features for characterization, instead of using only one parameter, especially in the case of heterogeneous lesions.

Keywords:
Cancer, Ultrasonography, Backscattering, Data sets, Medical image noise

Abstract:
Attenuation of ultrasound in tissue can be estimated from the propagating pulse center frequency downshift. This method assumes that the envelope of the emitted pulse can be approximated by a Gaussian function and that the attenuation linearly depends on frequency. The resulting downshift of the mean frequency depends not only on attenuation but also on pulse bandwidth and propagation distance. This kind of approach is valid for narrowband pulses and shallow penetration depth. However, for short pulses and deep penetration, the frequency downshift is rather large and the received spectra are modified by the limited bandwidth of the receiving system. In this paper, the modified formula modeling the mean frequency of backscattered echoes is presented. The equation takes into account the limitation of the bandwidth due to bandpass filtration of the received echoes. This approach was applied to simulate the variation of the mean frequency of the pulse propagating for both weakly and strongly attenuating media and for narrowband and wideband pulses. The behavior of both the standard and modified estimates of attenuation has been validated using RF data from a tissue-mimicking phantom. The ultrasound attenuation of the phantom, determined with a corrected equation, was close to its true value, while the result obtained using the original formula was lower by as much as 50% at a depth of 8 cm.

Keywords:
Tissue attenuation, frequency downshift, bandwidth limitation

Abstract:
Sonodynamic therapy (SDT) is a promising technique based on the ability of certain substances, called sonosensitizers, to sensitize cancer cells to non-thermal effects of low-energy ultrasound waves, allowing their destruction. Sonosensitization is thought to induce cell death by direct physical effects such as cavitation and acoustical streaming as well as by complementary chemical reactions generating oxygen free radicals. One of the promising sonosensitizers is 5-aminolevulinic acid (ALA) which upon selective uptake by cancer cells is metabolized and accumulated as protoporphyrin IX. The objective of the study was to describe ALA-mediated sonodynamic effects in vitro on a rat RG2 glioma cell line. Glioma cells, seeded at the bottom of 96-well plates and incubated with ALA (10 μg/ml) for 6 h, were exposed to the sinusoidal US pulses with a resonance frequency of 1 MHz, 1000 μs duration, 0.4 duty-cycle, and average acoustic power varying from 2 W to 6 W. Ultrasound waves were generated by a flat circular piezoelectric transducer with a diameter of 25 mm. Cell viability was determined by MTT assay. Structural cellular changes were visualized with a fluorescence microscope. Signs of cytotoxicity such as a decrease in cell viability, chromatin condensation and apoptosis were found. ALA-mediated SDT evokes cytotoxic effects of low intensity US on rat RG2 glioma cells in vitro. This cell line is indicated for further preclinical assessment of SDT in in vivo conditions.

Keywords:
5-aminolevulinic acid, sonodynamic therapy, rat RG2 glioma cells, cell viability

Abstract:
Texture of ultrasound images contain information about the properties of examined tissues. The analysis of statistical properties of backscattered ultrasonic echoes has been recently successfully applied to differentiate healthy breast tissue from the benign and malignant lesions. We propose a novel procedure of tissue characterization based on acquiring backscattered echoes from the heated breast. We have proved that the temperature increase inside the breast modifies the intensity, spectrum of the backscattered signals and the probability density function of envelope samples. We discuss the differences in probability density functions in two types of tissue regions, e.g. cysts and the surrounding glandular tissue regions. Independently, Pennes bioheat equation in heterogeneous breast tissue was used to describe the heating process. We applied the finite element method to solve this equation. Results have been compared with the ultrasonic predictions of the temperature distribution. The results confirm the possibility of distinguishing the differences in thermal and acoustical properties of breast cyst and surrounding glandular tissues.

Keywords:
medical ultrasound, temperature changes in vivo, breast tissue, ultrasonic temperature measurement

Abstract:
For centuries tissue palpation has been an important diagnostic tool. During palpation, tumors are felt as tissues harder than the surrounding tissues. The significance of palpation is related to the relationship between mechanical properties of different tissue lesions. The assessment of tissue stiffness through palpation is based on the fact that mechanical properties of tissues are changing as a result of various diseases. A higher tissue stiffness translates into a higher elasticity modulus. In the 90’s, ultrasonography was extended by the option of examining the stiffness of tissue by estimating the difference in backscattering of ultrasound in compressed and non-compressed tissue. This modality is referred to as the static, compression elastography and is based on tracking the deformation of tissue subjected to the slowly varying compression through the recording of the backscattered echoes. The displacement is estimated using the methods of cross-correlation between consecutive ultrasonic lines of examined tissue, so calculating the degree of similarity of ultrasonic echoes acquired from tissue before and after the compression was applied. The next step in the development of ultrasound palpation was to apply the local remote tissue compression by using the acoustic radiation force generated through the special beam forming of the ultrasonic beam probing the tissue. The acoustic radiation force causes a slight deformation the tissue thereby forming a shear wave propagating in the tissue at different speeds dependent on the stiffness of the tissue. Shear wave elastography, carries great hopes in the field of quantitative imaging of tissue lesions. This article describes the physical basis of both elastographic methods: compression elastography and shear wave elastography.

Keywords:
elastography, static sonoelastography, dynamic sonoelastography, ultrasonography

Abstract:
Quantitative ultrasound methods are widely investigated as a promising tool for tissue characterization. In this paper, a novel quantitative method is developed which can be used to assess scattering properties of tissues. The proposed method is based on analysis of oscillations of the backscattered echo power spectrum. It is shown that these oscillations of the power spectrum are connected with the distances between scatterers within the medium. Two techniques are proposed to assess the scatterer’s distribution. First, we show that the inverse Fourier transform of the backscattered echo power spectrum corresponds to a histogram of the distances between scatterers. Second, the Hilbert-Huang transform is used to directly extract the power spectrum oscillations. Both methods are examined by means of a numerical experiment. A cellular gas model of a biological medium is considered. Results are presented and discussed. Both methods can be used to evaluate the scatterer’s distribution by means of the power spectrum oscillations.

Keywords:
quantitative ultrasound, signal analysis, wave scattering

Abstract:
The aim of this work was to use the streaming phenomena to assist clot dissolution in blood vessel. Such treatment is called sonothrombolysis. Acoustic streaming is a steady flow in a fluid driven by the acoustic wave propagating in a lossy medium. It is a non-linear effect and it depends on ultrasound intensity, and sound absorption in the media.

The source of ultrasound was a flat piezoceramic disc generating long pulses at 1 MHz frequency and 0.2 W/cm2 ITA acoustical intensity. The streaming was generated in a vessel simulating free space, and next repeated in a multi-well cell culture plate, and in the limited space inside the 8 mm diameter silicone tube positioned perpendicular to the ultrasonic beam. The tube was filled with a mixture of water, glycerol, and starch, so with acoustic properties similar to blood. The streaming velocity was recorded either by the Siemens Acuson Antares ultrasonic scanner operating in the color Doppler mode at 8.9 MHz, or by the custom built 20 MHz pulsed Doppler flowmeter.

The results obtained using both systems were very similar. The recorded streaming velocities were 3.2 cm/s, 6.1 cm/s and 0.3 cm/s, respectively. They were an order of magnitude smaller than that calculated theoretically. However, the results obtained confirm existence of streaming, even very close to the source, in the limited space. This effect will be explored in in-vitro experiments of blood clot dissolution within the tube simulating a blood vessel.

Keywords:
ultrasound, radiation force, blood, thrombolysis

Abstract:
The purpose of this study was to evaluate the accuracy of statistical properties of the backscttered ultrasound in differential diagnosis of the breast lesions. The B-mode images together with the appropriate RF echoes from the breast lesions and surrounding tissues were collected. The RF data were processed for the statistics of the backscattered echo signals using K and Nakagami distributions characterized by the M and m parameters, respectively. Based on both, M and m parameters, a set of 18 parameters was derived.

From the point of view of the sensitivity of detection of the cancer the best score was obtained using maximum value of M parameter, the best specificity was received using the differential Nakagami parameter (the differential values between lesions and surrounding tissues). In conclusion the quantitative sonography is a method which has potential to be a complementary tool for classification of the breast lesions.

Keywords:
quantitative ultrasound, breast cancer, Nakagami distribution, K dstribution

Abstract:
Background:
There is a growing interest in the application of non-invasive clinical tools allowing one to assess the endothelial function, preceding atherosclerosis. The precision in estimating of the artery Flow Mediated Vasodilation (FMD) using standard 10-12 MHz linear array probes does not exceed 0.2 mm, far beyond that required.

Methods:
We have introduced a wide-band, high frequency 25-30 MHz, Golay encoded wobbling type imaging to measure dilation of the radial artery instead of the brachial one. 18 young volunteers, and 4 volunteers with cardiac events history, were examined. In the second approach 20 MHz linear scanning combined with 20 MHz pulsed Doppler attached to the linear array was used. The radial artery FMD was normalized using shear rate at the radial artery wall.

Results and Conclusions:
For the “healthy” group, the FMD resulting from reactive hyperemia response was over 20%; while in the “atherosclerotic” group, the FMD was at least twice as small, not exceeding 10%. The shear rate (SR) normalized FMDSR was in the range from 7.8 to 9.9 in arbitrary units, while in patients with minor cardiac history FMDSR was clearly lower, 6.8 to 7.6. The normalized FMDSR of radial artery RARR can be an alternative to the brachial FMD where the precision of measurements is lower and the diameter dilation does not exceed 7-10%.

Keywords:
thick film transducers, atherosclerosis, flow mediated vasodilation

Abstract:
Our goal in this study was to evaluate the relevance of shear wave sonoelastography (SWE) in the differential diagnosis of masses in the breast with respect to ultrasound (US). US and SWE were performed (Aixplorer System, SuperSonic Imagine, Aix en Provence, France) in 76 women (aged 24 to 85) with 84 lesions (43 malignant, 41 benign). The study included BI-RADS-US (Breast Imaging Reporting and Data System for Ultrsound) category 3–5 lesions. In elastograms, the following values were calculated: mean elasticity in lesions (Eav.l) and in fat tissue (Eav.f.) and maximal (Emax.adj.) and mean (Eav.adj.) elasticity in lesions and adjacent tissues. The sensitivity and specificity of the BI-RADS category 4a/4b cutoff value were 97.7% and 90.2%. For an Eav.adj. of 68.5 kPa, the cutoff sensitivity was 86.1% and the specificity was 87.8%, and for an Emax.adj. of 124.1 kPa, 74.4% and 92.7%, respectively. For BI-RADS-US category 3 lesions, Eav.l, Emax.adj. and Eav.adj. were below cutoff levels. On the basis of our findings, Eav.adj. had lower sensitivity and specificity compared with US. Emax.adj. improved the specificity of breast US with loss of sensitivity.

Keywords:
Breast ultrasound, Shear wave sonoelastography, Young's modulus, Focal breast lesions

Abstract:
A 30-MHz ultrasonic scanner was used to collect B-scan images together with appropriate radiofrequency echoes from diseased and healthy skin regions of patients with diagnosed basal cell carcinoma and pre-cancerous lesions (actinic keratosis). Radiofrequency data were processed to obtain the attenuation coefficient and statistics of the backscattered echo signal determination (K-distribution and effective density of scatterers [EDS]). The attenuation coefficient was significantly higher for patients with basal cell carcinoma than for healthy patients. Also, the pre-cancerous skin lesions had increased attenuation. The averaged EDS values for cancer lesions were significantly lower than those for pre-cancerous lesions and healthy skin. The successful differentiation between the tissue groups examined suggests the potential value of the attenuation coefficient and EDS for carcinoma characterization.

Keywords:
Quantitative ultrasound, High frequency, Human skin, Skin lesions, K-distribution, Attenuation coefficient, Tissue characterization

Abstract:
The goal of this study is to improve the synthetic transmit aperture (STA) imaging method by employing the transducer array element beam pattern correction combined with emission of mutually orthogonal complementary Golay sequences. The transmit-receive scheme based on simultaneous emission of different Golay pairs by adjacent transmit subapertures is implemented to decrease the image reconstruction time. A brief discussion on the fundamentals of the orthogonal Golay complementary sequences is provided and their advantages for the STA imaging method are demonstrated. The performance of the developed approach was tested using FIELD II simulated synthetic aperture data from the point reflectors, which allowed to estimate both; the penetration depth and the lateral resolution. In the work the 128 element, 5 MHz, linear array transducer was used. The obtained results showed that the applying the beam pattern correction leads to the image quality improvement in the vicinity of the transducer face. Specifically, the noise level evaluated between the point reflectors at the depth of 4 mm decreased from - 14.1 dB for the case of omnidirectional source to - 38.7 dB when the element beam pattern correction was implemented. The simulation proved that the overall imaging quality was improved considerably.

Keywords:
coded excitation, element directivity, mutually orthogonal Golay codes, synthetic aperture, ultrasound imaging

Abstract:
The main aim of this study was to verify the suitability of the hydrogel sonographic model of the left ventricle (LV) in the computed tomography (CT) environment and echocardiography and compare the radial strain calculations obtained by two different techniques: the speckle tracking ultrasonography and the multislices computed tomography (MSCT). The measurement setup consists of the LV model immersed in a cylindrical tank filled with water, hydraulic pump, the ultrasound scanner, hydraulic pump controller, pressure measurement system of water inside the LV model, and iMac workstation. The phantom was scanned using a 3.5 MHz Artida Toshiba ultrasound scanner unit at two angle positions: 0° and 25°. In this work a new method of assessment of RF speckles’ tracking. LV phantom was also examined using the CT 750 HD 64-slice MSCT machine (GE Healthcare). The results showed that the radial strain (RS) was independent on the insonifying angle or the pump rate. The results showed a very good agreement, at the level of 0.9%, in the radial strain assessment between the ultrasound M-mode technique and multislice CT examination. The study indicates the usefulness of the ultrasonographic LV model in the CT technique. The presented ultrasonographic LV phantom may be used to analyze left ventricle wall strains in physiological as well as pathological conditions. CT, ultrasound M-mode techniques, and author's speckle tracking algorithm, can be used as reference methods in conducting comparative studies using ultrasound scanners of various manufacturers.

Keywords:
Computed tomography, Echocardiography, Left ventricle, Speckles tracking, Strain, Ultrasound phantoms

Abstract:
Aim.
The aim of our study was to assess the usefulness of high frequency ultrasonography in the diagnosis of melanoma. Methods. We examined 84 patients with suspicious melanocytic skin lesions, including 19 cases of melanoma. In vivo high-resolution ultrasonography (30 MHz) was performed prior to excision.

Results.
In ultrasound scans early melanomas presented as flat oval or fusiform shaped structures and were clearly demarcated, while advanced melanomas were characterized by a roundish shape with less distinct borders. The ultrasonographic thickness of in situ melanomas ranged from 0.02 to 0.85 mm. In the case of invasive tumors, the mean thickness evaluated by high frequency ultrasonography was 10.7% higher compared to the Breslow Score (1.44±0.8 mm and 1.3±0.88 mm, respectively). In all melanomas of Breslow Score of 1 mm or more ultrasound also indicated a Breslow Score of 1 mm or more.

Conclusion.
High frequency ultrasound examination has limited value in differential diagnosis of melanoma, but it gives a clear picture of the size and depth of the tumor. The method should be used as a complementary method (after dermoscopy and, where applicable, reflectance confocal microscopy) in preoperative evaluation of the tumor. In some cases of locally advanced melanoma, ultrasound examination may allow to reduce the number of surgical procedures and favor the decision of a one-time surgical treatment (removal of primary tumor and sentinel lymph node biopsy at the same time).

Keywords:
Dermoscopy - Diagnosis - Melanoma - Microscopy, confocal - Ultrasonography

Abstract:
A tissue thermal conductivity (Ks) is an important parameter which knowledge is essential whenever thermal fields induced in selected organs are predicted. The main objective of this study was to develop an alternative ultrasonic method for determining Ks of tissues in vitro suitable for living tissues. First, the method involves measuring of temperature-time T(t) rises induced in a tested tissue sample by a pulsed focused ultrasound with measured acoustic properties using thermocouples located on the acoustic beam axis. Measurements were performed for 20-cycle tone bursts with a 2 MHz frequency, 0.2 duty-cycle and 3 different initial pressures corresponding to average acoustic powers equal to 0.7 W, 1.4 W and 2.1 W generated from a circular focused transducer with a diameter of 15 mm and f-number of 1.7 in a two-layer system of media: water/beef liver. Measurement results allowed to determine position of maximum heating located inside the beef liver. It was found that this position is at the same axial distance from the source as the maximum peak-peak pressure calculated for each nonlinear beam produced in the two-layer system of media. Then, the method involves modeling of T(t) at the point of maximum heating and fitting it to the experimental data by adjusting Ks. The averaged value of Ks determined by the proposed method was found to be 0.5±0.02 W/(m·°C) being in good agreement with values determined by other methods. The proposed method is suitable for determining Ks of some animal tissues in vivo (for example a rat liver).

Keywords:
Acoustics, Sound pressure, Beef, Thermal conductivity, Thermocouples, Nonlinear systems, Sound waves, Bioacoustics

Abstract:
In order to have consistent and repeatable effects of sonodynamic therapy (SDT) on various cancer cells or tissue lesions we should be able to control a delivered ultrasound energy and thermal effects induced. The objective of this study was to investigate viability of rat C6 glioma cells in vitro depending on the intensity of ultrasound in the region of cells and to determine the exposure time inducing temperature rise above 43°C, which is known to be toxic for cells. For measurements a planar piezoelectric transducer with a diameter of 20 mm and a resonance frequency of 1.06 MHz was used. The transducer generated tone bursts with 94 μs duration, 0.4 duty-cycle and initial intensity ISATA (spatial averaged, temporal averaged) varied from 0.33 W/cm2 to 8 W/cm2 (average acoustic power varied from 1 W to 24 W). The rat C6 glioma cells were cultured on a bottom of wells in 12-well plates, incubated for 24 h and then exposed to ultrasound with measured acoustic properties, inducing or causing no thermal effects leading to cell death. Cell viability rate was determined by MTT assay (a standard colorimetric assay for assessing cell viability) as the ratio of the optical densities of the group treated by ultrasound to the control group. Structural cellular changes and apoptosis estimation were observed under a microscope. Quantitative analysis of the obtained results allowed to determine the maximal exposure time that does not lead to the thermal effects above 43°C in the region of cells for each initial intensity of the tone bursts used as well as the threshold intensity causing cell death after 3 min exposure to ultrasound due to thermal effects. The averaged threshold intensity was found to be about 5.7 W/cm2.

Keywords:
Cancer cells, Photo-sensitizers, Sonodynamic therapy, Thermal effects, Ultrasonic beam properties

Abstract:
The soft tissue attenuation is an interesting parameter from medical point of view, because the value of attenuation coefficient is often related to the state of the tissue. Thus, the imaging of the attenuation coefficient distribution within the tissue could be a useful tool for ultrasonic medical diagnosis. The method of attenuation estimation based on tracking of the mean frequency changes in a backscattered signal is presented in this paper. The attenuation estimates are characterized by high variance due to stochastic character of the backscattered ultrasonic signal and some special methods must be added to data processing to improve the resulting images. The following paper presents the application of Spatial Compounding (SC), Frequency Compounding (FC) and the combination of both. The resulting parametric images are compared by means of root-mean-square errors. The results show that combined SC and FC techniques significantly improve the quality and accuracy of parametric images of attenuation distribution.

Keywords:
tissue attenuation estimation, parametric imaging, synthetic aperture, spatial compounding, frequency compounding

Abstract:
In the paper the concept of synthetic aperture used for high resolution/high frame rate ultrasonic imaging is reviewed. The synthetic aperture technique allows building extended “virtual” apertures, synthesized from smaller real aperture resulting in improved lateral resolution along full penetration depth without sacrificing the frame rate.

Especially, four methods, synthetic aperture focusing (SAF), multi-element synthetic aperture focusing (M-SAF), synthetic receive aperture (SRA) and synthetic transmit aperture (STA) are addressed. The effective aperture function, describing two-way, far field radiation is a useful tool in beam pattern analysis. Some basic notations, which are used to calculate the effective aperture are introduced in Appendix.

Keywords:
synthetic aperture, effective aperture, ultrasonography

Abstract:
The present work concerns the sonographic model of the left ventricle (LV) examined in the Computed Tomography (CT) environment and compare radial strain calculations obtained by two different techniques: the speckle tracking ultrasonography and the Multislices Computed Tomography (MSCT). The Left Ventricular (LF) phantom was fabricated from 10% solution of the poly(vinyl alcohol) (PVA). Our model of the LV was driven by the computer- controlled hydraulic piston Super -Pump (Vivitro Inc., Canada) with adjustable fluid volumes. The stroke volume was set at of 24ml. The fluid pressure was changed within range of 0- 60 mmHg, and the pulse rate was of 60 cycles/per minute. The relationships between computer controlled left ventricular wall deformations and its visual izations of the echocardiographic and CT imaging, both in the normal and pathological conditions were examined. The difference of assessment the Radial Strain between two methods was not exceeding 1.1%.

Abstract:
Sonodynamic therapy is the ultrasound dependent enhancement of the cytotoxic activities of certain drugs called sonosensitizers. The study of therapeutic efficacy of ultrasound is always preceded by in-vitro tests. In this work, two in-vitro sonication procedures were compared. One with the transducer positioned bellow the cell colony, radiating upward, with standing wave reflected from the water-air surface, the second, in the free field conditions. Efficiency of the cancer cells necrosis caused by ultrasound was compared with acoustical field intensity ISPTA measured by a hydrophone. The standing wave conditions effectively increased the intensity of the ultrasonic wave at the level of cells. To achieve 50% of cell viability, the intensity ISATA, decreased from 5.8 W/cm2 to 0.3 W/cm2. In summary, sonication in the standing wave conditions can effectively and reproducibly destroy cells by ensuring the sterility and without the risk of overheating.

Keywords:
ultrasound, sonodynamic therapy, cancer cells, necrosis

Abstract:
Nowadays there are new modalities in ultrasound imaging allowing better characterization of tissue regions with different stiffness. We are proposing a novel approach based on compression and rarefaction of tissue simultaneously with imaging. The propagating wave is a combination of two pulses. A low frequency pulse is expected to change the local scattering properties of the tissue due to compression/rarefaction while a high frequency pulse is used for imaging. Two transmissions are performed for each scanning line. First, with the imaging pulse that propagates on maximum compression caused by a low frequency wave. Next, the low frequency wave is inverted and the imaging pulse propagates over the maximum rarefaction. After the processing of the subtracted echoes from subsequent transmissions including wavelet transform and band-pass filtering, differential images were reconstructed. The low frequency wave has a visible impact on the scattering properties of the tissue which can be observed on a differential image.

Abstract:
This article has been prepared on the basis of the Ultrasonography Standards of the Polish Ultrasound Society (2011) and updated based on the latest findings and reports. Ultrasound examination of the lower extremity veins is relatively easy and commonly used to confirm or rule out venous thrombosis. However, a relatively easy compression test frequently requires experience, particularly in situations when imaging is difficult(due to lymphedema, dressing or thick tissues). The technique is time-consuming and requires assessment of each deep vein every 1 cm. Lesions in the deep veins cannot be ruled out when the vessels are assessed in only 2–3 points – a full examination is needed. The value of the method is the highest when the proximal section is assessed and the lowest when crural veins are evaluated. Doppler sonography is the basic method used when patients are prepared for a surgery of varicose veins. The assessment of the superficial veins prior to this procedure is tedious and requires knowledge of anatomy together with numerous variants. A considerable challenge is posed by re-assessment of recurrent varicose veins following a previous surgery. The Standards include anatomic nomenclature proposed by the Polish Society for Vascular Surgery and Polish Society of Phlebology, which should facilitate communication with clinicians. The most beneficial patient positions have been thoroughly discussed in terms of safety and effectiveness of the examination. Sometimes during such an examination, no venous pathology is found, but other changes with symptoms that suggest deep thrombophlebitis are detected. In such a situation, it is necessary to conduct an initial (or complete, if possible) assessment of lesions as well as provide recommendations connected with further, more detailed diagnosis.

Keywords:
venous thrombosis, veins, venous insufficiency, varicose veins, standards

Abstract:
Carcinoma of the prostate gland is the most common neoplasm in men. Its treatment depends on multiple factors among which local staging plays a significant role. The basic method is transrectal ultrasound imaging. This examination enables imaging of the prostate gland and its abnormalities, but it also allows ultrasound-guided biopsies to be conducted. A conventional gray-scale ultrasound examination enables assessment of the size, echostructure and outlines of the anatomic capsule, but in many cases, neoplastic lesions cannot be observed. For this reason, new sonographic techniques are implemented in order to facilitate detectability of cancer. The usage of contrast agents during transrectal ultrasound examination must be emphasized since, in combination with color Doppler, it facilitates detection of cancerous lesions by visualizing flow which is not observable without contrast enhancement. Elastography, in turn, is a different solution. It uses the differences in tissue elasticity between a neoplastic region and normal prostatic parenchyma that surrounds it. This technique facilitates detection of lesions irrespective of their echogenicity and thereby supplements conventional transrectal examinations. However, the size of the prostate gland and its relatively far location from the transducer may constitute limitations to the effectiveness of elastography. Moreover, the manner of conducting such an examination depends on the examiner and his or her subjective assessment. Another method, which falls within the novel, popular trend of combining imaging methods, is fusion of magnetic resonance imaging and transrectal sonography. The application of multidimensional magnetic resonance imaging, which is currently believed to be the best method for prostate cancer staging, in combination with the availability of a TRUS examination and the possibility of monitoring biopsies in real-time sonography is a promising alternative, but it is associated with higher costs and longer duration of the examination. This paper presents the most important novel trends in transrectal imaging in prostate cancer diagnosis based on the review of the articles available in the PubMed base and published after 2010.

Keywords:
transrectal ultrasound, TRUS, prostatic neoplasms, cancer of the prostate, neoplasm staging, elastography

Abstract:
A Doppler ultrasound examination has an advantage over other vessel imaging methods as it can be carried out by the patient’s bedside and allows to make a diagnosis without exposing the patient to the inconveniency of transportation or an X-ray scan. The purpose of testing the lower extremities and the aorta is to objectively confirm a preliminary clinical diagnosis, localize lesions responsible for the symptoms of the disease, determine their severity and nature (e.g., if they are calcifications or soft lesions), and finally evaluate the hemodynamic criteria. In assessment of the aorta attention is paid not only to aortic diameter measurements, but also to the vascular lumen (dissections with the formation of two flow channels, detachments, balloting of atherosclerotic plaques, etc.) and the presence of atherosclerotic plaques with influx into them (PAU – penetrating ulcer in the plaque or lesions surrounding the aorta, such as retroperitoneal fibrosis or mycotic aneurysm). A correct diagnosis of an abdominal aortic aneurysm requires repeated measurements of the abdominal aorta diameter, and in particular its transverse dimension. When assessing the degree of peripheral arterial stenosis on the basis of hemodynamic parameters, degree of morphological stenosis must be taken into consideration. Collateral circulation may reduce the flow through the main vessel, and thus, the achieved systolic velocities are lower and may understate the degree of the assessed stenosis. Calf vessels are difficult to detect, which results both from the thickness of the muscle and the presence of calcifications. This article has been prepared on the basis of Standards of the Polish Ultrasound Society (2011) and updated on the basis of the latest reports from relevant literature.

Keywords:
Doppler examination, lower limb arteries, abdominal aorta, the size of stenosis, atherosclerotic plaque, ulceration in the atherosclerotic plaque, recommendations

Abstract:
Measurement of the shear elastic constant of soft and highly damping tissue of high Poisson ratio is quite a challenging task. It is proposed to evaluate shear wave velocity and damping of tissue by measuring the shear skimming bulk waves using one interdigitated interdigital transducer on a piezoelectric layer, such as polyvinylidene fluoride, applied to the surface of the small tissue sample.

Keywords:
Interdigital transducer, surface acoustic waves, electrostatics, mixed boundary-value problem

Abstract:
The paper presents the modified multi-element synthetic transmit aperture (MSTA) method for ultrasound imaging. It is based on coherent summation of RF echo signals with apodization weights taking into account the finite size of the transmit subaperture and of the receive element. The work presents extension of the previous study where the modified synthetic transmit aperture (STA) method was considered and verified [1]. In the case of MSTA algorithm the apodization weights were calculated for each imaging point and all combinations of the transmit subaperture and receive element using their angular directivity functions (ADFs). The ADFs were obtained from the exact solution of the corresponding mixed boundary-value problem for periodic baffle system modeling the transducer array. Performance of the developed method was tested using Field II simulated synthetic aperture data of point reflectors for 4 MHz 128-element transducer array with 0.3 mm pitch and 0.02 mm kerf to estimate the visualization depth and lateral resolution. Also experimentally determined data of the tissue-mimicking phantom (Dansk Fantom Service, model 571) obtained using 128 elements, 4 MHz, linear transducer array (model L14-5/38) and Ultrasonix SonixTOUCH Research platform were used for qualitative assessment of imaging contrast improvement. Comparison of the results obtained by the modified and conventional MSTA algorithms indicated 15 dB improvement of the noise reduction in the vicinity of transducer’s surface (1 mm depth), and concurrent increase in the visualization depth (86% augment of the scattered amplitude at the depth of 90 mm). However, this increase was achieved at the expense of minor degradation of the lateral resolution of approximately 8% at the depth of 50 mm and 5% at the depth of 90 mm.

Keywords:
Synthetic aperture imaging, Ultrasound imaging, Directivity function, Beamforming

Abstract:
For the last 20 years the world cardiosurgery has presented a considerable change of attitude to mechanical circulatory support. In spite of technological progress the main problems in ventricular assist devices are: thrombosis and low accuracy of flow measurements. In this paper the prototype of multi-gate Doppler flowmeter intended for cardiac assist system ReligaHeart EXT has been presented as well as the possibility of ultrasonic micro embolus detection.

Keywords:
artificial heart, microemboli, ultrasound Doppler

Abstract:
We explain, motivation behind this work and briefly describe foundation of new method which we have developed for efficient solution in PC environment of the nonlinear propagation equation with the boundary conditions applied for both circular and not circular transducers (like array). Comparison between new and old method will be presented for strongly nonlinear disturbance. At the end we will demonstrate the results of the numerical calculations of the nonlinear field propagating from the array.

Keywords:
Nonliear propagation, Envelope waves, Fast calculations

Abstract:
Two different tissue phantoms of the left ventricle to imitate a beating left ventricle were developed: first was prepared using a sponge material and second phantom was constructed using a polyvinyl alcohol material modeled into a homogeneous hollow cylinder: approximately 10 cm and 12 cm in length for the first and second phantom, respectively. Both phantoms were 5 cm in diameter, with a wall thickness of 1.0 cm. Additionally, a small part of the wall of the second phantom was processed to simulate the stiffness of myocardial infarction. The phantoms were connected at the end to an adjustable external pump. The pulse volume inside the cylinder was set between 12 to 50 ml at rates of 40, 60, 100, 120 beats/minute. The phantoms were immersed in water for ultrasound scanning with two different insonation angles (90 and 65 degrees). Strain and strain rate were measured with different combinations of angles and pulse rates. The main aim of this work was to develop the new method for validation of the human infarct wall strain calculation procedures using the speckles tracking.

Keywords:
soft tissue, phantom, ultrasound

Abstract:
The purpose of the research was to evaluate the role of high frequency ultrasound in monitoring and efficacy assessment of anti-cellulite treatments. A group of 66 women used 3 different types of anti-cellulite treatments; additionally a placebo group (n = 18) was created. The μ-Scan ultrasound device with a 35 MHz mechanical probe was used for the examinations. The following parameters were subjected to the ultrasound evaluation: epidermis thickness, dermis thickness, dermis echogenicity, the length and area of subcutaneous tissue bands projecting into the dermis (dermis-hypodermis junction), as well as the presence/absence of edema within the dermis. As a result of anti-cellulite treatment, the length and area of dermis-hypodermis junction significantly decreased, and dermis echogenicity significantly increased. Ultrasound imaging made it possible to evaluate the efficacy of the applied treatments. The high frequency ultrasound is a useful imaging technique for the application in aesthetic dermatology and cosmetology.

Keywords:
Aesthetic Medicine, Cellulite, Anti-Cellulite Treatment, High Frequency Ultrasound, Skin Ultrasound

Abstract:
A dedicated ultrasonic scanner for acquiring RF echoes backscattered from the trabecular bone was developed. The design of device is based on the goal of minimizing of custom electronics and computations executed solely on the main computer processor and the graphics card. The electronic encoder-digitizer module executing all of the transmission and reception functions is based on a single low-cost field programmable gate array (FPGA). The scanner is equipped with a mechanical sector-scan probe with a concave transducer with 50 mm focal length, center frequency of 1.5 MHz and 60% bandwidth at −6 dB. The example of femoral neck bone examination shows that the scanner can provide ultrasonic data from deeply located bones with the ultrasound penetrating the trabecular bone up to a depth of 20 mm. It is also shown that the RF echo data acquired with the scanner allow for the estimation of attenuation coefficient and frequency dependence of backscattering coefficient of trabecular bone. The values of the calculated parameters are in the range of corresponding in vitro data from the literature but their variation is relatively high.

Keywords:
cancellous bone, broadband ultrasound attenuation, FPGA

Abstract:
Background
Cellulite affects nearly 85% of the female population. Given the size of the phenomenon, we are continuously looking for effective ways to reduce cellulite. Reliable monitoring of anticellulite treatment remains a problem.

Objective
The main aim of the study was to evaluate the effectiveness of anticellulite treatment carried out using radiofrequency (RF), which was monitored by classical and high-frequency ultrasound.

Methods
Twenty-eight women underwent anticellulite treatment using RF, 17 women were in the placebo group. The therapy was monitored by classical and high-frequency ultrasound. The examinations evaluated the thickness of the epidermal echo, dermis thickness, dermis echogenicity, the length of the subcutaneous tissue bands growing into the dermis, the presence or absence of oedema, the thickness of subcutaneous tissue as well as thigh circumference and the stage of cellulite (according to the Nurnberger–Muller scale).

Results
Cellulite was reduced in 89.286% of the women who underwent RF treatment. After the therapy, the following observations were made: a decrease in the thickness of the dermis and subcutaneous tissue, an increase in echogenicity reflecting on the increase in the number of collagen fibres, decreased subcutaneous tissue growing into bands in the dermis, and the reduction of oedema. In the placebo group, no statistically significant changes of the above parameters were observed.

Conclusion
Radiofrequency enables cellulite reduction. A crucial aspect is proper monitoring of the progress of such therapy, which ultrasound allows.

Keywords:
anticellulite treatment, high-frequency ultrasound

Abstract:
The modified synthetic transmit aperture (STA) algorithm is described. The primary goal of this work was to assess the possibility to improve the image quality achievable using synthetic aperture (SA) approach and to evaluate the performance and the clinical applicability of the modified algorithm using phantoms. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point in the image and for all possible combinations of the transmit–receive pairs. The weights are calculated using the angular directivity functions of the transmit–receive elements, which are approximated by a far-field radiation pattern of a narrow strip transducer element vibrating with uniform pressure amplitude over its width. In this way, the algorithm takes into account the finite aperture of each individual element in the imaging transducer array. The performance of the approach developed was tested using FIELD II simulated synthetic aperture data of the point reflectors, which allowed the visualization (penetration) depth and lateral resolution to be estimated. Also, both simulated and measured data of cyst phantom were used for qualitative assessment of the imaging contrast improvement. The experimental data were obtained using 128 elements, 4 MHz, linear transducer array of the Ultrasonix research platform. The comparison of the results obtained using the modified and conventional (unweighted) STA algorithms revealed that the modified STA exhibited an increase in the penetration depth accompanied by a minor, yet discernible upon the closer examination, degradation in lateral resolution, mainly in the proximity of the transducer aperture. Overall, however, a considerable (12 dB) improvement in the image quality, particularly in the immediate vicinity of the transducer’s surface was demonstrated. The modified STA method holds promise to be of clinical importance, especially in the applications where the quality of the ‘‘near-field’’ image, that is the image in the immediate vicinity of the scanhead is of critical importance such as for instance in skin- and breast-examinations.

Keywords:
synthetic aperture imaging, ultrasound imaging, directivity function, beamforming

Abstract:
The purpose of this work was to evaluate ultrasound modality as a non-invasive tool for determination of impact of the degree of the atherosclerotic plaque located in human internal carotid arteries on the values of the parameters of the pulse wave. Specifically, the applicability of the method to such arteries as brachial, common, and internal carotid was examined. The method developed is based on analysis of two characteristic parameters: the value of the mean reflection coefficient modulus |Γ|a of the blood pressure wave and time delay Δt between the forward (travelling) and backward (reflected) blood pressure waves. The blood pressure wave was determined from ultrasound measurements of the artery’s inner (internal) diameter, using the custom made wall tracking system (WTS) operating at 6.75 MHz. Clinical data were obtained from the carotid arteries measurements of 70 human subjects. These included the control group of 30 healthy individuals along with the patients diagnosed with the stenosis of the internal carotid artery (ICA) ranging from 20% to 99% or with the ICA occlusion. The results indicate that with increasing level of stenosis of the ICA the value of the mean reflection coefficient measured in the common carotid artery, significantly increases from |Γ|a = 0.45 for healthy individuals to |Γ|a = 0.61 for patients with stenosis level of 90–99%, or ICA occlusion. Similarly, the time delay Δt decreases from 52 ms to 25 ms for the respective groups. The method described holds promise that it might be clinically useful as a non-invasive tool for localization of distal severe artery narrowing, which can assist in identifying early stages of atherosclerosis especially in regions, which are inaccessible for the ultrasound probe (e.g. carotid sinus or middle cerebral artery).

Keywords:
Pulse wave, Ultrasound, Vascular impedance, Stenosis

Abstract:
The main objective of this study is to develop an echocardiographic model of the left ventricular and numerical modeling of the speckles- markers tracking in the ultrasound (ultrasonographic) imaging of the left ventricle. The work is aimed at the creation of controlled and mobile environment that enables to examine the relationships between left ventricular wall deformations and visualizations of these states in the form of echocardiographic imaging and relations between the dynamically changing distributions of tissue markers of studied structures.

Keywords:
left ventricle, echocardiography, speckle modeling, ultrasound phantoms, strain, strain rate

Abstract:
The paper presents the optimization problem for the multi-element synthetic transmit aperture method (MSTA) in ultrasound imaging applications. The optimal choice of the transmit aperture size is made as a trade-off between the lateral resolution, penetration depth and the frame rate. Results of the analysis obtained by a developed optimization algorithm are presented. The maximum penetration depth and lateral resolution at given depths are chosen as optimization criteria. The results of numerical experiments carried out in MATLAB using synthetic aperture data of point reflectors obtained by the FIELD II simulation program are presented. The visualization of experimental synthetic aperture data of a tissue mimicking phantom and in vitro measurements of the beef liver performed using the SonixTOUCH Research system are also shown.

Keywords:
ultrasound imaging, synthetic aperture, beamforming

Abstract:
The paper presents a classification of the healthy skin and the skin lesions (basal cell carcinoma) basing on a statistics of the envelope of ultrasonic echoes. The echoes envelopes distributions were modeled using Rayleigh and K-distribution. The distributions were compared with empirical data to find which of them better models the statistics of the echo-signal obtained from the human skin. The results indicated that the K-distribution provides a better fit. Also, a characteristic parameter of the K-distribution, the effective number of scatterers (M), was investigated. The values of the M parameter, obtained for the skin cancer (basal cell carcinoma), were lower as compared to those obtained for the healthy skin. The results indicate that the statistical quantitative ultrasound parameters have a potential for extracting information useful for characterization of the skin condition.

Keywords:
statistics, K-distribution, Rayleigh distribution, ultrasonic scattering, human dermis

Abstract:
An analytical model of imaging using synthetic aperture (SA) methods is presented. This model takes into account: fundamental features of an environment, of an electric transmission/reception path and a description of SA structure - possible schemes of transmission, reception and image formation. Then two schemes are analyzed: a proposed cumulative synthetic transmit aperture (CSTA) and for comparison of the standard STA schemes. For both methods identical basic parameters - equal sequences of transmit and receive transducers were applied. The distinctive feature of CSTA is gathering (summing up) echoes of subsequent transmissions in one acquisition mat ix sufficient for image reconstruction. In traditionally applied STA methods a separate acquisition matrix for each transmission is created. Therefore there are a dozen to several dozen more matrices and the time of image reconstruction is at least several times longer than in CSTA. The presented experimental results obtained using wire and tissue mimicking phantoms have shown the comparable imaging quality in both methods.

Keywords:
ultrasound imaging, synthetic aperture

Abstract:
Ultrasonic imaging is a well-established technique in medicine. However, in most conventional applications of clinical ultrasonic scanners only the peak amplitude echogenicity is used to create the image. Moreover, signal envelope detection destroys potentially useful information about frequency dependence of acoustic properties of tissue comprised in RF backscattered echoes. We have explored the possibility of developing the method of imaging the distribution of the acoustic attenuation in tissue. We expect that the method will help in localization of the pathological states of tissue including tumors and diffuse liver diseases. The spatial resolution and precision of the method are crucial for medical diagnosis, hence the synthetic aperture technique was applied for ultrasonic data collection. The final goal of the presented project is to develop reliable diagnostic tool, which could be implemented in standard USG systems, as the new visualization mode.

Keywords:
soft tissue parametric imaging, attenuation imaging, synthetic aperture focusing technique

Abstract:
Propagation of ultrasonic waves in the tissue is sensitive to the alternation of tissue composition and structure.. This paper presents the classification of healthy skin and skin lesions (basal cell carcinoma (BCC)) based on statistic parameters of the envelope of echosignal. The statistics of envelope of the ultrasonic signal was modeled using Rayleigh and non-Rayleigh (the K-distribution) statistics. Furthermore the characteristic parameter of K-distribution, the effective number of scaterrers (M) was investigated.
Comparison of the results obtained for region of the skin where the BCC was diagnosed and the regions of healthy skin has shown differences in the values of M parameter. These results indicate that this parameter has the potential for extracting information useful for characterizing skin lesions.

Keywords:
high frequency, ultrasound, basall cell carcinoma, ststistics

Abstract:
In the paper the study of synthetic transmit aperture method applying the Golay coded transmission for medical ultrasound imaging is presented. Longer coded excitation allows to increase the total energy of the transmitted signal without increasing the peak pressure. Moreover signal-to-noise ratio and penetration depth are improved while maintaining high ultrasound image resolution. In the work the 128-element linear transducer array with 0.3 mm inter-element spacing excited by one cycle and the 8 and 16- bit Golay coded sequences at nominal frequency 4 MHz was used. To generate a spherical wave covering the full image region a single element transmission aperture was used and all the elements received the echo signals. The comparison of 2D ultrasound images of the tissue mimicking phantom and in vitro measurements of the beef liver is presented to illustrate the benefits of the coded transmission. The results were obtained using the synthetic aperture algorithm with transmit and receive signals correction based on a single element directivity function.

Keywords:
Golay coded sequences, radiation pattern, signal, processing, synthetic aperture, ultrasound imaging

Abstract:
The paper presents the study of synthetic transmit aperture method applying the Golay coded transmission for medical ultrasound imaging. Longer coded excitation allows to increase the total energy of the transmitted signal without increasing the peak pressure. Signal-to-noise ratio and penetration depth are improved maintaining high ultrasound image resolution. In the work the 128-element linear transducer array with 0.3 mm inter-element spacing excited by one cycle and the 8 and 16-bit Golay coded sequences at nominal frequencies 4 MHz was used. Single element transmission aperture was used to generate a spherical wave covering the full image region and all the elements received the echo signals. The comparison of 2D ultrasound image s of the wire phantom as well as of the tissue mimicking phantom is presented to demonstrate the benefits of the coded transmission. The results were obtained using the synthetic aperture algorithm with transmit and receive signals correction based on a single element directivity function

Keywords:
Golay coded sequences, radiation pattern, synthetic aperture, ultrasound imaging

Abstract:
The paper presents the optimization problem for the multi-element synthetic transmit aperture method (MSTA) in ultrasound imaging applications. The optimal choice of the transmit aperture size is performed as a trade-off between the lateral resolution, penetration depth and the frame rate. Results of the analysis obtained by a developed optimization algorithm are presented. Maximum penetration depth and the best lateral resolution at given depths are chosen as the optimization criteria. The optimization algorithm was tested using synthetic aperture data of point reflectors simulated by Filed II program for Matlab® for the case of 5MHz 128-element linear transducer array with 0.48 mm pitch are presented. The visualization of experimentally obtained synthetic aperture data of a tissue mimicking phantom and in vitro measurements of the beef liver are also shown. The data were obtained using the SonixTOUCH Research systemequipped with a linear 4MHz 128 element transducerwith 0.3 mm element pitch, 0.28 mm element width and 70% fractional bandwidth was excited by one sine cycle pulse burst of transducer's center frequency.

Keywords:
synthetic aperture method, ultrasound imaging, beamforming

Abstract:
The paper describes the investigations intended to compare the results of experimental measurements f backscattering properties of the trabecular bone with the results of computer simulations. Ultrasonic RF echoes were collected using two bone scanners operating at 0.58 and 1.3 MHz. The simulations of the backscattered RF echoes were performed using the scattering model of the trabecular bone that consisted of cylindrical and spherical elements uniformly distributed in waterlike medium. For each measured or simulated RF backscatter the statistical properties of the signal envelope were determined. Experimental results suggest deviations of the backscattering properties from the Rayleigh distribution. The results of simulation suggest that deviation from Rayleigh distribution depends on the variation of trabeculae diameters and the number of thin trabeculae. Experimentally determined deviations corresponded well to the deviations calculated from simulated echoes assuming trabeculae thickness variation equaled to the earlier published histomorphometric study results.

Keywords:
trabecular bone, scattering statistics, bone model

Abstract:
The integral equations that describe scattering in the media with step-rise changing parameters have been numerically solved for the trabecular bone model. The model consists of several hundred discrete randomly distributed elements. The spectral distribution of scattering coefficients in subse- quent orders of scattering has been presented. Calculations were carried on for the ultrasonic frequency ranging from 0.5 to 3 MHz. Evaluation of the contribution of the first, second, and higher scattering orders to total scattering of the ultrasounds in trabecular bone was done. Contrary to the approaches that use the lCT images of trabecular structure to modeling of the ultrasonic wave propagation condition, the 3D numerical model consisting of cylindrical elements mimicking the spatial matrix of trabeculae, was applied. The scattering, due to interconnections between thick trabeculae, usually neglected in trabecular bone models, has been included in calculations when the structure backscatter was evaluated. Influence of the absorption in subsequent orders of scattering is also addressed. Results show that up to 1.5 MHz, the influence of higher scattering orders on the total scattered field characteristic can be neglected while for the higher frequencies, the relatively high amplitude interference peaks in higher scattering orders clearly occur.

Keywords:
Multiple scattering, Complex media, Bone

Abstract:
Background: The development of ultrasonography allowed for skin imaging used in dermatology and esthetic medicine. By means of classic and high-frequency ultrasonographies, changes within the dermis and subcutaneous tissue can be presented.
Objective: The aim of this study was to show the possibi­lities of applying classic and high-frequency ultrasonogra­phies in esthetic dermatology based on monitoring various types of anti-cellulite therapies.
Methods: Sixty-one women with cellulite were assigned to two smaller groups. One group was using anti-cellulite cream and the second group was a placebo group. The ultrasound examin;ition was carried out before the initiation and after the completion of the treatment and evaluated epidermal echoes, the thickness of the subcutaneous tissue and the dermis, dermis echogenicity, the length and surface rea of the subcutaneous tissue fascicles growing into the dermis, and the presence or absence of edemas.
Results: After the completion of the treatment, a statistically significant difference was observed. The most useful para­meters were as follows: the thickness of the subcutaneous tissue, echogenicity, the surface area and length of the sub­cutaneous tissue, as well as the presence of edemas. The discussed changes were not observed in the placebo group.
Conclusion: Classic and high-frequency ultrasonographies are useful methods for monitoring anti-cellulite therapies.

Keywords:
high-frequency ultrasonography - cellulite classic ultrasonography ultrasonography

Abstract:
This work addresses the difficulties in the measurements of the nonlinear medium parameter B/A and presents a modification of the finite amplitude method (FAM), one of the accepted procedures to determine this parameter. The modification is based on iterative, hybrid approach and entails the use of the versatile and comprehensive model to predict distortion of the pressure–time waveform and its subsequent comparison with the one experimentally determined. The measured p–t waveform contained at least 18 harmonics generated by 2.25 MHz, 29 mm effective diameter, single element, focused PZT source (f-number 3.5) and was recorded by Sonora membrane hydrophone calibrated in the frequency range 1– 40 MHz. The hydrophone was positioned coaxially at the distal end of the specially designed, two-section assembly comprising of one, fixed length (60 mm), water-filled cylindrical container and the second, variable length (60–120 mm) container that was filled with unknown medium. The details of the measurement chamber are described and the reasons for this specific design are analyzed. The data were collected with the variable length chamber filled with 1.3-butanediol, which was used as a close approximation of tissue mimicking phantom. The results obtained provide evidence that a novel combination of the FAM with the semi-empirical nonlinear propagation model based on the hyperbolic operator is capable of reducing the overall uncertainty of the B/A measurements as compared to those reported in the literature. The overall uncertainty of the method reported here was determined to be ±2%, which enhances the confidence in the numerical values of B/A measured for different, clinically relevant media. Optimization of the approach is also discussed and it is shown that it involves an iterative procedure that entails a careful selection of the acoustic source and its geometry and the axial distance over which the measurements need to be performed. The optimization also depends critically on the experimental determination of the source surface pressure amplitude.

Keywords:
pulsed finite-amplitude acoustic waves, nonlinear propagation, nonlinearity parameter B/A

Abstract:
The attenuating properties of biological tissue are of great importance in ultrasonic medical imaging. Investigations performed in vitro and in vivo showed the correlation between pathological changes in the tissue and variation of the attenuation coefficient. In order to estimate the attenuation we have used the downshift of mean frequency (fm) of the interrogating ultrasonic pulse propagating in the medium. To determine the fm along the propagation path we have applied the fm estimator (I/Q algorithm adopted from the Doppler mean frequency estimation technique). The mean-frequency shift trend was calculated using Single Spectrum Analysis. Next, the trends were converted into attenuation coefficient distributions and finally the parametric images were computed. The RF data were collected in simulations and experiments applying the synthetic aperture (SA) transmit-receiving scheme. In measurements the ultrasonic scanner enabling a full control of the transmission and reception was used. The resolution and accuracy of the method was verified using tissue mimicking phantom with uniform echogenicity but varying attenuation coefficient.

Keywords:
tissue attenuation imaging, synthetic aperture, diagnosis enhancing

Abstract:
The paper presents the theoretical and experimental study of synthetic transmit aperture (STA) method combined with Golay coded transmission for medical ultrasound imaging applications. The transmission of long waveforms characterized by a particular autocorrelation function allows to increase the total energy of the transmitted signal without increasing the peak pressure. It can also improve signal-to-noise ratio and increase the visualization depth maintaining the ultrasound image resolution.
In the work the 128-element linear transducer array with 0.3 mm pitch excited by the 8 and 16-bits Golay coded sequences as well as a one cycle at nominal frequencies 4 MHz were used. The comparison of 2D ultrasound images of the tissue mimicking phantoms is presented to demonstrate the benefits of coded transmission. The image reconstruction was performed using synthetic STA algorithm with transmit and receive signals correction based on a single element directivity function.

Keywords:
ultrasound imaging, synthetic aperture, beamforming, radiation pattern, coded sequences, Golay codes

Abstract:
Recently a new technology of piezoelectric transducers based on PZT thick film has been developed as a response to a call for devices working at higher frequencies suitable for production in large numbers at low cost. Eight PZT thick film based focused transducers with resonant frequency close to 40 MHz were fabricated and experimentally investigated. The PZT thick films were deposited on acoustically engineered ceramic substrates by pad printing. Considering high frequency and nonlinear propagation it has been decided to evaluate the axial pressure field emitted (and reflected by thick metal plate) by each of concave transducer differing in radius of curvature – 11 mm, 12 mm, 15 mm, 16 mm.
All transducers were activated using AVTEC AVG-3A-PS transmitter and Ritec diplexer connected directly to Agilent 54641D oscilloscope. As anticipated, in all cases the focal distance was up to 10% closer to the transducer face than the one related to the curvature radius. Axial pressure distributions were also compared to the calculated ones (with the experimentally determined boundary conditions) using the angular spectrum method including nonlinear propagation in water. The computed results are in a very good agreement with the experimental ones. The transducers were excited with Golay coded sequences at 35–40 MHz. Introducing the coded excitation allowed replacing the short-burst transmission at 20 MHz with the same peak amplitude pressure, but with almost double center frequency, resulting in considerably better axial resolution. The thick films exhibited at least 30% bandwidth broadening comparing to the standard PZ 27 transducer, resulting in an increase in matching filtering output by a factor of 1.4–1.5 and finally resulting in a SNR gain of the same order.

Keywords:
transducers, thick film, high frequency ultrasound, pulse compression, Golay codes

Abstract:
Many therapeutic applications of pulsed focused ultrasound are based on heating of detected lesions which may be localized in tissues at different depths under the skin. In order to concentrate the acoustic energy inside tissues at desired depths a new approach using a planar multi-element annular array transducer with an electronically adjusted time-delay of excitation of its elements, was proposed. The 7-elements annular array transducer with 2.4 MHz center operating frequency and 20 mm outer diameter was produced. All its elements (central disc and 6 rings) had the same radiating area. The main purpose of this study was to investigate thermal fields induced in bovine liver in vitro by pulsed focused ultrasonic beams with various acoustic properties and electronically steered focal plane generated from the annular array transducer used. The measurements were performed for the radiating beams with the 20 mm focal depth. In order to maximize nonlinear effects introducing the important local temperature rise, the measurements have been performed in two-layer media comprising of a water layer, whose thickness was specific for the transducer used and equal to 13 mm, and the second layer of a bovine liver with a thickness of 20 mm. The thickness of the water layer was determined numerically as the axial distance where the amplitude of the second harmonics started to increase rapidly. The measurements of the temperature rise versus time were performed using a thermocouple placed inside the liver at the focus of the beam. The temperature rise induced in the bovine liver in vitro by beams with the average acoustic power of 1W, 2W, and 3W and duty cycle of 1/5, 1/15 and 1/30, respectively, have been measured. For each beam used the exposure time needed for the local tissue heating to the temperature of 43◦C (used in therapies based on ultrasonic enhancement of drug delivery or in therapies involving stimulation of immune system by enhancement of the heat shock proteins expression) and to the temperature of 56◦C (used in HIFU therapies) was determined. Two sets of measurements were done for each beam considered. First, the thermocouple measurement of the temperature rise was done and next, the real-time monitoring of dynamics of growth of the necrosis area by using ultrasonic imaging technique, while the sample was exposed to the same acoustic beam. It was found that the necrosis area becomes visible in the ultrasonic image only for beams with the average acoustic power of 3 W, although after cutting the sample the thermally ablated area was visible with the naked eye even for the beams with lower acoustic power. The quantitative analysis of the obtained results allowed to determine the exposure time needed to get the necrosis area visible in the ultrasonic image.

Keywords:
annular array transducer, pulsed focused nonlinear ultrasound, electronically moved focus, tissue heating, biological effects, tissue necrosis

Abstract:
Typical diagnostic process in dermatology includes clinical assessment, dermoscopic and histopathologic examination. Microsonography was initiated in seventies and much progress in the development of high-frequency scanners occurred since that time. The aim of the study was the assessment of high frequency ultrasonography in dermatologic diagnostics. Material and methods. Examination was performed with 30 MHz ultrasound transducer with 0,1 mm resolution and 7 mm penetration. We examined patients with benign and malignant neoplasms, cicatrical alopecia and morphea. Results. Sonographically, the normal skin is composed of three layers: an epidermal entry echo, dermis and subcutaneous tissue. In healthy skin we can image small hypoechoic areas which correspond to hair folicules, vessels and sebaceous glands. Most of small skin neoplasmatic lesions were hypoechogenic and homogeneous on examination. Extensive lesions were multicomponent with normo-, hypo- and anechogenic structures. The assessment of lesion’s boarders allows sometimes to conclude the invasiveness of the lesion. Areas of skin with clinically visible atrophy showed diffuse increasing of echogenicity. In early lesions, without accomplished fibrosis, diffuse decreasing of echogenicity can be observed, that is probably caused by inflammatory infiltration. In comparison to the healthy skin, the ultrasound scan of sclerotic skin shows a wide entry echo and highly reflective, thicker dermis as a result of the collagen fibers accumulation. Conclusions. Above data suggest that ultrasonographic examination may be a valuable dermatologic diagnostic tool that completes classical dermatologic diagnostics and helps to plan the treatment.

Keywords:
high frequency ultrasonography, benign neoplasms, malignant neoplasms, cicatrical alopecia, morphea

Abstract:
Some important details of the Backscatter Effective Cross-Sections (BECS) obtained for random scattering structures (like trabecular bone) are explain by comparison with the results obtained by means of the simplified theoretical model. The simplified model was (establish) and justified on the basis of the structural analysis of the results obtained for exact model of the field scattering on complex structures. The simplified model is commonly used in description of the scattering on the regular structures like crystal. Comparison with experimental results for the trabecular bone is also presented. The results allowed to conclude that crystallographic methods could be potentially useful for extracting characteristic features of trabecular bone.

Keywords:
Multi scattering, Random structures

Abstract:
The paper presents the multi-element synthetic transmit aperture (MSTA) method with a small number of elements transmitting and all elements receiving apertures in medical ultrasound imaging. Compared to other methods the MSTA allows to increase the system frame rate and provides the best compromise between penetration depth and lateral resolution.
In the experiments a 128-element linear transducer array with 0.3 mm inter-element spacing and a burst pulse of 125 ns duration were used. The comparison of 2D ultrasound images of tissue mimicking phantom obtained using the STA and the MSTA methods is presented to demonstrate the benefits of the second method. The obtained results were performed using SA algorithm with transmit and receive signals correction based on a single element directivity function.

Keywords:
beamforming, frame rate, synthetic aperture, ultrasound imaging

Abstract:
The mean frequency correlation estimator and SSA technique were implemented for processing of the RF ultrasonic echoes. The estimated attenuation values were equal to 0.7 and 0.9 dB/(MHz∙cm) and agreed well with the real values. We have found the RF data obtained using synthetic aperture technique (SA) to be much more reliable in terms of attenuation extraction then echoes recorded using the standard delay and sum (DAS) beamforming. The imaging of attenuation in tissue seems to be a promising technique in medical diagnostics, although the precision of a single scan is often unsatisfactory.

Keywords:
tissue attenuation imaging, sythetic aperture focusing technique

Abstract:
The pathological states of biological tissue are often resulted in attenuation changes. Thus, information about attenuating properties of tissue is valuable for the physician and could be useful in ultrasonic diagnosis. We are currently develop ing a technique for parametric imaging of attenuation and we intend to apply it for in vivo characterization of tissue. The attenuation estimation method based on the echoes mean frequency changes due to tissue attenuation dispersion, is presented. The Doppler IQ technique was adopted to estimate the mean frequency directly from the raw RF data. The Singular Spectrum Analysis technique was used for the extraction of mean frequency trends. These trends were converted into atten uation distribution and finally the parametric images were computed. In order to reduce variation of attenuation estimates the spatial compounding method was applied. Operation and accuracy of attenuation extracting procedure was verified by calculating the attenuation coefficient distribution using the data from the tissue phantom (DFS, Denmark) with uniform echogenicity while attenuation coefficient underwent variation.

Keywords:
ultrasound attenuation estimation, spatial compounding, parametric imaging

Abstract:
A trabecular bone consists of trabeculae whose mechanical properties differ significantly from the surrounding marrow, therefore an ultrasonic wave propagating within the bone structure is strongly scattered. The aim of this paper was to evaluate the contribution of the first, second and higher order scattering (multiple scattering) into the total scattering of ultrasound in a trabecular bone. The scattering due to the interconnections between thick trabeculae, usually neglected in trabecular bone models, has been also studied. The basic element in our model of the trabecular bone was an elastic cylinder with a various finite-length and diameter as well as orientation. The applied model was taking into account variation of both, elements size and their spatial configuration. The field scattered on the bone model was evaluated by solving numerically the integral form of the generalized Sturm-Liouville equation describing a scalar wave in inhomogeneous and lossy media. For the scattered fields calculated numerically the effective cross-sections were determined. The influence of absorption on the scattering coefficients was demonstrated. The results allowed to conclude that within the frequency range from 0.5 to 1.5 MHz contribution of the second order scattering to the effective backscattering cross-section is at least 500 times lower than that due to the first order scattering. It was noticed that for a frequency higher than 1.5 MHz fast growth of the backscattering (reflection) coefficients, calculated for the second order scattering, occurs.

Keywords:
multi-scattering, random complex structures, trabecular bone model

Abstract:
Synthetic aperture (SA) technique is a novel approach to present day commercial systems and has previously not been used in medical ultrasound imaging. The basic idea of SA is to combine information acquired simultaneously from all directions over a number of emissions and to reconstruct the full image from these data. The paper presents the multi-element STA (MSTA) method for medical ultrasound imaging. The main difference with the STA approach is the use of a few elements in the transmit mode in contrast to a single element aperture. This allows increasing the system frame rate, decreasing the number of emissions, and provides the best compromise between the penetration depth and lateral resolution. Besides, a modified MSTA is proposed with a corresponding RF signal correction in the receive mode, which accounts for the element directivity property. In the experiments a 32-element linear transducer array with 0.48 mm interelement spacing and a burst pulse of 100 ns duration were used. Two elements wide transmission aperture was used to generate an ultrasound wave covering the full image region. The comparison of 2D ultrasound images of a tissue mimicking phantom obtained using the STA and MSTA methods is presented to demonstrate the benefits of the second one.

Keywords:
ultrasound imaging, synthetic aperture, beamforming

Abstract:
The use of therapeutic ultrasound continues to grow. A focused ultrasonic wave can increase the tissue temperature locally for the non-invasive cancer treatment or other medical applications. The authors have designed a seven-element annular array transducer operating at 2.4 MHz. Each element was excited by sine burst supplied by a linear amplifier and FPGA control circuits. The acoustic field, generated by a transducer was initially numerically simulated in a computer and next compared to water tank hydrophone measurements performed at 20, 40 and 60 mm focal depth. The results showed good agreement of the measurements with theory and the possibility to focus the ultrasound in the preselected area. The total acoustic power radiated by the annular array was equal to 2.4W.

Keywords:
ultrasonic therapy, annular array transducer, ultrasonic field

Abstract:
Ultrasonic methods of human body internal structures imaging are being continuously enhanced. New algorithms are created to improve certain output parameters. A synthetic aperture method (SA) is an example which allows to display images at higher frame-rate than in case of conventional beam-forming method. Higher computational complexity is a limitation of SA method and it can prevent from obtaining a desired reconstruction time. This problem can be solved by neglecting a part of data. Obviously it implies a decrease of imaging quality, however a proper data reduction technique would minimize the image degradation. A proposed way of data reduction can be used with synthetic transmit aperture method (STA) and it bases on an assumption that a signal obtained from any pair of transducers is the same, no matter which transducer transmits and which receives. According to this postulate, nearly a half of the data can be ignored without image quality decrease. The presented results of simulations and measurements with use of wire and tissue phantom prove that the proposed data reduction technique reduces the amount of data to be processed by half, while maintaining resolution and allowing only a small decrease of SNR and contrast of resulting images.

Keywords:
ultrasonic imaging, synthetic transmit aperture, data reduction, effective aperture, reciprocity

Abstract:
Signals scattered in trabecular bone contain information about properties of the bone structure. Evaluation of this properties may be essential for osteoporosis diagnosis and treatment monitoring because the standard densitometry does not provide complete information about the bone strength. It was previously demonstrated that using numerical model of backscattering in trabecular bone it is possible to estimate some microstructural characteristics of bone. Model predicts departures from the Rayleigh statistics of the scattered signal envelope depended on the scatterer physical parameters and its shape uniformity. This study concerns examination of trabecular bone (calcaneus) in vivo. Ultrasonic bone scanner operating at frequency of 1,5 MHz was used to collect backscattered signals. Data were processed in order to obtain the statistical properties of the signal envelope and to compare them with histograms resulting from modeling. This study is an approach towards developing a tool for the investigation of scattering in trabecular bone that can potentially provide clinically useful information about bone strength and condition.

Keywords:
bone structure, bone properties, calcaneus

Abstract:
Ultrasonography (USG) is a widespread and powerful tool used successfully in modern diagnostics. The standard USG scanner reflects impedance variations within the tissue that is penetrated by the ultrasound pulse. Although such image provides a lot of information to the physician, there are another parameters which could be imaged. The attenuation coefficient is one of them. Imaging of attenuation seems to be a promising tool for ultrasonic medical diagnostics. The attenuation estimation method based on the echoes mean frequency changes due to tissue attenuation dispersion is presented. The Doppler IQ technique is adopted to estimate the mean frequency changes directly from the raw RF data. The Singular Spectrum Analysis (SSA) technique is used for the mean frequency trend extraction. The changes of the mean frequency trend are related directly to the local attenuation coefficient. Preliminary results of the tissue phantom attenuation coefficient estimation and imaging using the commercial scanner are presented.

Keywords:
tissue attenuation imaging, ultrasound attenuation estimation

Abstract:
Beneficial biological effects in soft tissues can be induced by focused ultrasound of low intensity (LIFU). For example, increasing of cells immunity to stress can be accomplished through the enhanced heat shock proteins (Hsp) expression induced by the low intensity focused ultrasound. The possibility to control the Hsp expression enhancement in soft tissues in vivo can be the potential new therapeutic approach to neurodegenerative diseases that utilizes the known feature of cells to increase their immunity to stresses through the Hsp expression enhancement. The controlling of the Hsp expression enhancement by adjusting the level of exposure to ultrasound energy would allow evaluating of ultrasound-mediated treatment efficiency. Our objective was to develop the numerical model capable of predicting in space and time temperature fields induced in multilayer nonlinear attenuating media by a circular focused transducer generating pulsed acoustic waves and to compare the results calculated for two-layer configuration of media: water - fresh rat liver with the experimental data. The measurements of temperature variations versus time at 5 points on the acoustic beam axis within the tissue sample were performed using 0.2-mm diameter thermocouples. Temperature fields were induced by the transducer with 15-mm diameter, 25-mm focal length and 2-MHz centre frequency generating tone bursts with the intensity ISPTA varied between 0.45 W/cm2 and 1.7 W/cm2 and duration varied between 20 and 500 cycles at the same 20-% duty cycle and 20-min exposure time. Quantitative analysis of the obtained results allowed to show that, for example, for the acoustic beam with intensity ISPTA = 1.13 W/cm2 exposure time to ultrasound should not be longer than 10 min to avoid cells necrosis following the 43-oC temperature threshold exceeding.

Keywords:
low intensity focused ultrasound, soft tissues, temperature fields, ultrasonic regimes, therapy efficiency

Abstract:
The scattering of ultrasonic waves depends on the size, shape, acoustical properties and concentration of scatterers in tissue. In these study K distribution of the ultrasound backscatter envelope was used to assess the structural properties of the skin tissue. The custom-designed high frequency ultrasonic scanner was applied to obtain RF B-scans of the skin in vivo at the frequency of 20-30MHz.
The results are encouraging. The K distribution models the envelope statistics very well. The parameters of the K-distribution, namely, the effective number of scatterers may be useful for the skin characterization.

Keywords:
skin characterization, ultrasound, K distribution

Abstract:
The Synthetic Aperture (SA) methods are widespread and successfully used in radar technology, as well as in the sonar systems. The advantages of high framerate and its relatively good resolution in the whole area of scanning, make this technique an object of interest in medical imaging methods such as ultrasonography (US). This paper describes the possible usage of the SA method in ultrasound imaging. The introduction to the principles of the SA technique in ultrasonography is presented. The measurements of different SA schemes were conducted using the set-up consisting of the research ultrasonograph module, the PC and the special wire phantom. The results for different schemes of image reconstruction are presented. Particularly the Synthetic Transmit Aperture (STA) technique was concerned. Results of the STA method are discussed in this paper.

Keywords:
synthetic aperture focusing technique, ultrasonic imaging

Abstract:
The work describes the use of a synthetic transmit aperture (STA) with a single element transmitting and all elements receiving in medical ultrasound imaging. STA technique is a novel approach to today’s commercial systems, where an image is acquired sequentially one image line at a time that puts a strict limit on the frame rate and the amount of data needed for high image quality. The STA imaging allows to acquire data simultaneously from all directions over a number of emissions, and the full image can be reconstructed.
In experiments a 32-element linear transducer array with 0.48 mm inter-element spacing was used. Single element transmission aperture was used to generate a spherical wave covering the full image region. The 2D ultrasound images of wire phantom are presented obtained using the STA and commercial ultrasound scanner Antares to demonstrate the benefits of the SA imaging.

Keywords:
ultrasound imaging, synthetic aperture, frame rate, beamforming

Abstract:
The paper describes the computer simulations allowing investigating the properties of the ultrasound pulse-echo signal, as it is received on the transducer surface after scattering in trabecular bone. A novel computer simulation model provides better understanding of ultrasonic scattering in porous bone structure and it can be also used to yield an ideal environment in which, the effects of various parameters (scatterer mechanical and geometrical properties, scatterer’ concentration), the shape of incident wave and experimental conditions influencing the scattering of ultrasonic waves in trabecular bone structure can be examined individually. The results proved that the computer simulation has a particular relevance in studying scattering in cancellous bone which may be approximated as a collection of two populations of scatterers, cylindrical and spherical that imitate thick and thin trabeculae respectively.

Keywords:
bone modeling, scattering simulation, osteoporosis, trabecular bone

Abstract:
A clinically applicable method for noninvasive measurement of hematocrit based on 20 MHz multigate Doppler ultrasound was developed. The ultrasound attenuation coefficient in blood is obtained by measuring the power of the signal coming from gates at different depths. A robust averaging method is introduced, which provides stable and repeatable results by using the echo signals from all depths inside the vessel. In vitro measurements have been done on porcine blood with hematocrit ranging from 3.0% to 65.0%. Steady and pulsatile flow conditions have been simulated using a peristaltic pump. The attenuation coefficient indicated the linear relation to hematocrit. The resulting correlation coefficient was R=0.999 for the continuous blood flow and R=0.992 for pulsatile flow. In vivo measurements have been performed in the brachial artery in 43 patients with hematocrit in the range of 32.0% to 49.3%. The mean absolute error has been 3.24% with a standard deviation of 3.72%.

Keywords:
blood, hematocrit, Doppler, ultrasonic attenuation

Abstract:
The paper describes the use of synthetic transmit aperture (STA) imaging in medical ultrasound. The synthetic aperture (SA) imaging is a novel approach to today's commercial systems. In these systems the image is acquired sequentially one image line at a time that puts a strict limit on the frame rate and the possibility of acquiring a sufficient amount of data for high image quality. This limitation can be lifted by employing SA imaging where the data are acquired simultaneously from all directions over a number of emissions, and the full image can be reconstructed from those data. Due to the complete data set, it is possible to have full transmitting and receiving focusing at the entire image region to improve the contrast dynamic and spatial resolution. The paper describes the STA imaging with a single element transmitting and all elements receiving apertures. In experiments, 32-element linear transducer array with 0.48 mm inter-element spacing and a burst pulse of 100ns duration were used. The single element transmission aperture was used to generate a spherical wave covering the full image region. The 2D ultrasound images of wire phantom are presented to demonstrate the benefits of SA imaging.

Keywords:
ultrasound imaging, synthetic aperture, beamforming

Abstract:
The subject of this paper is a new software simulating ultrasound signal scattered on moving blood cells during Doppler examination of blood flow velocity using pulsed technique. Generated data are used for optimization and validation of Doppler signals processing algorithms.
The algorithm is based on the finite elements method FEM. A rigorous set of postulates which simplifies physics of modeled phenomenon enables to quicken the program significantly while preserving important properties (from application point of view) of generated signal.
The paper includes description of Doppler RF signal generation algorithm. The simplifying postulates are listed together with resulting signal fidelity degradation. Finally generated raw data is presented together with its Doppler Audio and Color processed version.
The signal processing results enable to reconstruct correctly the velocity profile and its time dependence. The results clearly confirm that the data generated by the algorithm are suitable for Doppler signals processing.

Keywords:
RF signal simulation, scattering on blood cells, pulsed Doppler

Abstract:
The scattering of ultrasonic waves depends on the size, shape, acoustical properties and concentration of scatterers in the tissue. The spectrum of the ultrasonic backscatter can be used to characterize non-invasively the structural and mechanical properties of tissue. We intend to apply the custom-designed high-frequency ultrasonic scanner for the skin and cutaneous lesions characterization by evaluating their attenuating and scattering properties. In this pilot study, we have explored the possibility of extracting the human skin backscattering coefficient (BC) from the ultrasonic B-scans obtained in vivo at 20–30 MHz. The measured BC values of normal skin (dermis) agree well with the published data. We have found also that the spatial resolution of the BC determination using our scanner is sufficient (aprox. 1 mm2) to characterize small skin lesions and assess their penetration depth.

Keywords:
attenuation coefficient, backscattering coefficient, dermis

Abstract:
The attenuating properties of biological tissue are of great importance in ultrasonic examination even though its anatomical variability limits diagnostics effectiveness. We are currently developing a technique for parametric imaging of attenuation and we intend to apply it for in vivo characterization of tissue. The diagnostic usefulness of the proposed technique crucially depends on the precision of the attenuation estimate and the resolution of the parametric image. These two parameters are highly correlated, since the resolution is reduced whenever averaging is used to minimize the errors introduced by the random character of the backscatter. Here we report on the results of numerical processing of both, simulated and recorded from a tissue-mimicking phantom echoes. We have analyzed the parameters of the estimation technique and examined their influence on the precision of the attenuation estimate and on the parametric image resolution. The optimal selection of attenuation image parameters depending on its intended diagnostic use, was also considered.

Keywords:
ultrasound attenuation, spatial resolution, parametric imaging

Abstract:
The aim of this work is twofold. Firstly, to verify a theoretical model which is capable of predicting temperature fields appearing in soft tissues during their ultrasound treatment. Secondly, to analyze some aspects of the dynamics of Heat Shock Response induced by the heating process in the context of therapeutic treatment. The theoretical investigations and quantitive analysis of temperature increments at any field point versus time of heating process, depending on the heat source power, spatial distribution and duration as well as on the tissue thermal properties, has been carried out by Finite Element Method (FEM). The validation of the numerical model has been performed by comparison of the calculation results with the experimental data obtained by measuring in vitro of the 3D temperature increments induced in samples of the turkey and veal liver by the circular focused transducer with the diameter of 15 mm, focal length of 25 mm and resonance frequency of 2 MHz. Various ultrasonic regimes were considered. They were controlled by adjusting ultrasound power and exposure time. The heat shock proteins (HSP) and misfolded proteins (MFP) levels during the proposed cyclic sonification are presented.

Keywords:
heat-responsive gene therapy, temperature field, low-power focused ultrasound, soft tissues, ultrasonic regime control, heat sources distribution, heat shock proteins

Abstract:
In this paper a new method utilizing nonlinear properties of tissues to improve contrast-to-noise ratio is presented. In our novel method the focused circular transducer is excited with two-tone bursts (including the 2.2 MHz fundamental and 4.4 MHz second harmonic frequencies) with specially coded polarization of each tone. This new approach was named Multitone Nonlinear Coding (MNC) because the choice of both tones polarization and amplitude law, allowing optimization of the probe receiving properties, depends on nonlinear properties of tissue. The numerical simulations of nonlinear fields in water and in tissue-like medium with absorption coefficient of 7 Np/(m•MHz) are performed. The comparison between the proposed method and the Pulse Inverse (PI) method is presented. The concept of the virtual fields was introduced to explain properties of both the Pulse Inversion and MNC methods and to compare their abilities. It was shown that for the same on-source pressure an application of the MNC method allows to decrease the mechanical index about 40 %, to improve lateral resolution from 10 to 30 % and to gain the signal-to-noise ratio up to 8 times with respect to the PI method.

Keywords:
harmonic imaging, ultrasonography, nonlinear propagation

Abstract:
Ultrasound is safe, convinient and inexpensive modality which may be useful for soft tissues treatment. A range of beneficial biological effects induced by ultrasound depends on the exposure level used during treatment. At high intensities instantaneous tissue necrosis is desired, whereas at lower intensities remedial reversible cellular effects may be produced. For example, increasing of cell immunity against stress can be obtained through the heat shock proteins (Hsp) expression enhancement. The possibility of the Hsp expression enhancement in soft tissues in vivo by means of controlled exposure to ultrasound would allow to evaluate the treatment efficiency. Ultrasonic regimes can be controlled by adjusting the ultrasound intensity, frequency, pulse duration, duty-cycle and exposure time. The goal of this work was to develop the numerical model capable of predicting in space and time the temperature fields induced by circular focused transducer generating tone bursts in multilayer nonlinear attenuating media, which is intended for the Hsp expression enhancement therapeutic applications. The acoustic pulsed pressure field generated by the transducer was calculated using our original 3D numerical solver [1]. For prediction of the temperature distributions in multilayer biological media the Pennes bio-heat transfer equation was solved numerically. The 3D thermal fields induced in a rat liver in vitro by a 2 MHz transducer of 15-mm diameter and 25-mm focal length during ultrasonic Hsp expression enhancement treatment using various acoustic beam intensities and exposure time was predicted.

Keywords:
multilayer biological media, ultrasound exposure parameters, local thermal fields, numerical prediction

Abstract:
Integral equations that describe scattering on the structure with step like abruptly changing physical parameters, have been numerically solved on example of the trabecular bone model. The model consists of several hundred elements with randomly selected parameters. The spectral distribution of scatter coefficients in subsequent orders - first second and third- of scattering has been presented.

Keywords:
Multiple scattering in absorbing medium, Complex random structure, Back scatter coefficients

Abstract:
Coded transmission is an approach to solve the inherent compromise between penetration and resolution required in ultrasound imaging. Our goal was to examine the applicability of the coded excitation to HF (20–35MHz) ultrasound imaging. A novel real-time imaging system for research and evaluation of the coded transmission was developed. The digital programmable coder-digitizer module based on the field programmable gate array (FPGA) chip supports arbitrary waveform coded transmission and RF echoes sampling up to 200MSPS, as well as real-time streaming of digitized RF data via a high speed USB interface to the PC. All RF and image data processing was implemented in the software. A novel balanced software architecture supports real-time processing and display at rates up to 30 frames/sec. The system was used to acquire quantitative data for sine burst and 16-bit Golay code excitation at 20MHz fundamental frequency. SNR gain close to 14 dB was obtained. The example of the skin scan clearly shows the extended penetration and improved contrast when 35MHz Golay code is used. The presented system is a practical and low cost implementation of coded excitation technique in HF ultrasound imaging that can be used as a research tool as well as to be introduced into production.

Keywords:
high frequency ultrasound, coded transmission, pulse compression, RF signal processing

Abstract:
The primary goal of this work was to verify experimentally the applicability of the recently introduced time-averaged wave envelope (TAWE) method as a tool for fast prediction of four dimensional (4D) pulsed nonlinear pressure fields from arbitrarily shaped acoustic sources in attenuating media. The experiments were performed in water at the fundamental frequency of 2.8 MHz for spherically focused (focal length F = 80 mm) square (20mm x 20 mm) and rectangular (10mm x 25 mm) sources similar to those used in the design of 1D linear arrays operating with ultrasonic imaging systems. The experimental results obtained with 10-cycle tone bursts at three different excitation levels corresponding to linear, moderately nonlinear and highly nonlinear propagation conditions (0.045, 0.225 and 0.45 MPa on-source pressure amplitude, respectively) were compared with those yielded using the TAWE approach. The comparison of the experimental results and numerical simulations has shown that the TAWE approach is well suited to predict (to within ± 1 dB) both, the spatial–temporal and spatial–spectral pressure variations in the pulsed nonlinear acoustic beams. The obtained results indicated that implementation of the TAWE approach enabled shortening of computation time in comparison with the time needed for prediction of the full 4D pulsed nonlinear acoustic fields using a conventional (Fourier-series) approach. The reduction in computation time depends on several parameters, including the source geometry, dimensions, fundamental resonance frequency, excitation level as well as the strength of the medium nonlinearity. For the non-axisymmetric focused transducers mentioned above and excited by a tone burst corresponding to moderately nonlinear and highly nonlinear conditions the execution time of computations was 3 and 12h, respectively, when using a 1.5 GHz clock frequency, 32-bit processor PC laptop with 2 GB RAM memory, only. Such prediction of the full 4D pulsed field is not possible when using conventional, Fourier-series scheme as it would require increasing the RAM memory by at least 2 orders of magnitude.

Keywords:
rectangular focused apertures, pulsed acoustic fields, nonlinear distortion, numerical modelling and experiments

Abstract:
Two 3.7 MHz focused ultrasonic transducers were built. One without backing and the second loaded on back. The primary application of the first transducer is Doppler blood flow measuring ultrasonic devices, the second is most useful for the B-mode imaging devices. The electrical and acoustical properties were tested and finally the results of the different Golay code excitations were compared. Efficiency of the not backed transducer was 4.1 dB higher. The not backed transducer performed maximum sensitivity for 8 bit two periods per bit code excitation. The backed transducer achieved maximum axial resolution for 16 bit one period per bit excitation.

Keywords:
ultrasonic transducers, imaging, backing, coded excitation, Golay codes

Abstract:
This study investigates a new composing method of double transmission of short coded sequences based on well-known Golay complementary codes, which allow to obtain the higher signal-to-noise ratio (SNR) and increase penetration depth. The proposed method can potentially find application in small parts ultrasonography and play important role in examination of superficial structures, e.g. in dermatology, ophthalmology, etc., where using longer coded sequences leads to increase of a dead zone and single pulse transmission of short sequences does not assure sufficient SNR. This paper discusses the comparison of results obtained during the examination of four different lengths pairs of Golay coded sequences excited at 3.7 MHz: the single 64-bits pair of Golay sequences and combined sequences consisting of two 8-, 16-, and 32-bits Golay codes separated in time. The experimental results have shown that using the double pulse transmission allows to suppress considerably the noise level, the SNR increases by 5.7 dB in comparison with the single pulse transmission of Golay sequences of the same length. The results of this work indicate that double pulse transmission enhances SNR while maintaining the dead zone short.

Keywords:
Golay complementary sequences, double pulse transmission, dead zone

Abstract:
The paper describes the synthetic transmit aperture (STA) imaging system with a single element transmitting and multi-element reception in medical ultrasound. Synthetic aperture method allows to achieve high electronic signal-to-noise ratio and good contrast resolution. A laboratory setup for acquisition of RF signals from linear transducer array was built. Simulated multichannel acquisition by multiplexing individual transducer was performed. In experiments 32-element linear transducer array with 0.48 mm inter-element spacing and a burst pulse with time duration 100 ns was used. Single element in the transducer transmitting aperture was used to generate a spherical wave covering the full image region. The echo signals were sampled independently by individual elements for each transmission. The comparison of 2D ultrasound images of wire phantom obtained using STA method and standard linear array scanning with commercial ultrasonograph is given. The results show excellent image resolution of the STA method and its robustness to refraction, attenuation and multiple reflection of ultrasound waves.

Keywords:
ultrasound imaging, synthetic aperture, contrast resolution

Abstract:
The goal of this work was to verify experimentally the applicability of the recently developed Time-Averaged Wave Envelope (TAWE) method [1] as a tool for fast prediction of pulsed nonlinear pressure fields from focused nonaxisymmetric acoustic sources in attenuating media. The experiments were performed in water at the fundamental frequency of 2.8 MHz for spherically focused (focal length F = 80 mm) square (20 x 20 mm) and rectangular (10 x 25 mm) sources similar to those used in the design of 1D linear arrays operating with ultrasonic imaging systems. The experimental results obtained with 10-cycle tone bursts at three different excitation levels corresponding to linear, moderately nonlinear and highly nonlinear propagation conditions (0.045, 0.225 and 0.45 MPa on-source pressure amplitude, respectively) were compared with those yielded using the TAWE approach. Comparison of the experimental and numerical calculations results has shown that the TAWE approach is well suited to predict (to within ± 1 dB) both the spatial-temporal and spatial-spectral pressure variations in the pulsed nonlinear acoustic beams.

Keywords:
rectangular focused apertures, pulsed acoustic fields, nonlinear distortion, numerical modelling

Abstract:
A new Acoustic Microscope operating at the frequency up to 200 MHz and allowing for visualization of the internal structures of materials was developed. The system was built basing on the commercially available components and the self-designed acoustic lenses. The dedicated software was developed to control the process of 3D RF-data acquisition, processing and presenting in 2D cross-sections or 3D surface rendering mode. This article describes the technical principles of the constructed microscope and presents the reconstructed images of the designed test-probe and of the integrated circuit.

Keywords:
Acoustic Microscopy, SAM, 3D imaging, rendering, subsurface imaging

Abstract:
An influence effect of fractional bandwidth of ultrasound imaging transducer on the gain of compressed echo signal being the complementary Golay sequences (CGS) with different spectral widths is studied in this paper. Also, a new composing transmission method of CGS is discussed together with compression technique applied in order to increase the signal-to-noise ratio (SNR) and penetration.
The CGS with two different bit lengths, one-cycle and two-cycles are investigated. Two transducers with fractional bandwidth of 25% and 80% at centre frequency 6 MHz are used. The experimental results are presented, clearly proofing that increasing of the code length leads to compressed echo amplitude enhancement. The smaller the bandwidth is the larger is this effect; the pulse-echo sensitivity of the echo amplitude increases by 1.88 for 25% fractional bandwidth and 1.47 for 80% while preserving time resolution. The presented results of double transmission of short codes show the penetration and SNR improvement while maintaining dead zone.

Keywords:
ultrasound, transducer, bandwidth, Golay code

Abstract:
We present a new method that uses nonlinear properties of tissue to improve contrast-to-noise ratio.
In our novel method, the acoustic source is activated with two tone-bursts (2.2 and 4.4 MHz), with specially designed polarization of the individual tone-burst. This new approach is called multitone nonlinear coding (MNC) because the choice of polarization of both tones (and their amplitudes), allowing optimization of the receiving properties, depends on the nonlinear properties of tissue. The calculations were done for two tone-bursts propagating in the tissue-like glossy medium with absorption of 7 Np/m · MHz. The method was experimentally verified by scanning the incident pulses propagating in soft tissue and by scanning the thread phantom immersed in water. The concept of the virtual fields was introduced to explain abilities and properties of pulse inversion and MNC and to compare the two methods. Comparison of the spatial field distribution obtained using MNC with the conventional harmonic imaging approach, in which the second harmonic is used to reconstruct the image, is presented. It was shown that, for the same peak pressure amplitude, the resulting mechanical index was about 40% lower for MNC, lateral resolution was 10% to 30% better and, what seems to be the most encouraging, the signal gain was up to eight times higher than pulse inversion.

Keywords:
harmonic imaging, ultrasonography, nonlinear propagation

Abstract:
Coded ultrasonography is intensively studied in many laboratories due to its remarkable properties, particularly increased penetration depth and signal-to-noise ratio (SNR). However, no data on the spatial behavior of the pressure field generated by coded bursts transmissions in the tissue were yet reported. This paper reports the results of investigations of the field structure in water, in degassed beef liver and in pork tissue using four different excitations signals, two and 16 periods sine bursts and sinusoidal sequences with phase modulation using 13-bits Barker code and 16-bits Golay complementary codes. The results of measured pressure field distributions before and after compression were compared with those recorded using short pulse excitation.

Keywords:
Coded excitation, Ultrasound field distribution, Matching filtering

Abstract:
In contrast to previously published papers [A. Nowicki, Z. Klimonda, M. Lewandowski, J. Litniewski, P.A. Lewin, I. Trots, Comparison of sound fields generated by different coded excitations – Experimental results, Ultrasonics 44 (1) (2006) 121–129; J. Litniewski, A. Nowicki, Z. Klimonda, M. Lewandowski, Sound fields for coded excitations in water and tissue: experimental approach, Ultrasound Med. Biol. 33 (4) (2007) 601–607], which examined the factors influencing the spatial resolution of coded complementary Golay sequences (CGS), this paper investigates the effect of ultrasound imaging transducer’s fractional bandwidth on the gain of the compressed echo signal for different spectral widths of the CGS. Two different bit lengths were considered, specifically one and two cycles. Three transducers having fractional bandwidth of 25%, 58% and 80% and operating at frequencies 6, 4.4 and 6 MHz, respectively were examined (one of the 6 MHz sources was focused and made of composite material). The experimental results have shown that by increasing the code length, i.e. decreasing the bandwidth, the compressed echo amplitude could be enhanced. The smaller the bandwidth was the larger was the gain; the pulse-echo sensitivity of the echo amplitude increased by 1.88, 1.62 and 1.47, for 25%, 58% and 80% bandwidths, respectively. These results indicate that two cycles bit length excitation is more suitable for use with bandwidth limited commercially available imaging transducers. Further, the time resolution is retained for transducers with two cycles excitation providing the fractional bandwidth is lower than approximately 90%. The results of this work also show that adjusting the code length allows signal-to-noise-ratio (SNR) to be enhanced while using limited (less that 80%) bandwidth imaging transducers. Also, for such bandwidth limited transducers two cycles excitation would not decrease the time resolution, obtained with ‘‘conventional’’ spike excitation. Hence, CGS excitation could be successfully implemented with the existing, relatively narrow band imaging transducers without the need to use usually more expensive wideband, composite ones.

Keywords:
ultrasound imaging, transducer bandwidth, complementary Golay sequences

Abstract:
The aim of this work is to explore and analyze the influence of the transducer bandwidth on the compressed echoes resulted from the Golay complementary codes transmission. For that reason, a computer simulation and experimental verification were performed that reflected the influence of the transducer bandwidth on the distortion of a signal. This study helps to elucidate why the echoes ringing is present for narrow bandwidth transducers. As known, the shape and symmetry of the pulse waveform and its interaction with the transducer bandwidth and its tuning circuitry have a profound effect on the pulse echo performance achievable from a medical scanning probe. The computer simulation was performed using the Matlab software for different fractional transducer bandwidths - from wideband transducers of 100% (ideal case), 90%, 75% to narrowband ones of 50% and 25%. The 16-bits Golay complementary sequences at nominal frequency of 1 MHz were used to illustrate the transducer bandwidth influence on the resulted signal. It was shown that the decreasing of the transducer bandwidth results in a considerable drop of the amplitude of the compressed echoes from 20.1 V for the 90% fractional bandwidth down to: 17.1 V, 12.5 V and 6.6 V for 75%, 50% and 25% bandwidths, respectively. The widths of the compressed echoes were widening at the same time from 708 ns up to 2.38 μs reducing the axial resolution from about 1 mm to over 3.6 mm. In the experiments, two transducers with different fractional bandwidths of 70% and 35% and nominal frequencies of 4.8 MHz and 6 MHz, respectively, were used.

Keywords:
transducer, signal analysis, distortion, filtering, Golay sequences

Abstract:
Coded transmission is a technique to solve the inherent compromise between penetration and resolution required in ultrasound imaging. Our aim was to examine the performance of the coded excitation in HF (20–35 MHz) ultrasound imaging. For this purpose a novel realtime imaging system has been developed. The digital programmable coder-digitizer module supports arbitrary coded waveform generation and RF echoes sampling up to 200 MSPS. All digital RF and image processing was implemented in software. The system performance was evaluated with a single thick-film transducer (focused 25 MHz, 75% bandwidth) scanning head. The RF echoes were acquired from a perfect reflector located with 1 cm of tissue mimicking material. Single sinus burst and 16-bits Golay codes excitations were evaluated. SNR gain for the Golay codes (referenced to single burst) of 15 dB for 20 MHz and 16 dB for 35 MHz were obtained. The axial resolution measured at half maximum was 35 ns for 20 MHz and 25 ns for 35 MHz for both single burst and the Golay codes. It clearly shows that the Golay codes can perfectly restore the resolution while giving respectable SNR gain.

Keywords:
medical imaging, coded excitation, high frequency ultrasound, digital signal processing

Abstract:
A standard USG image is in fact a visualization of a distribution of the reflexion coefficients. There is an increasing interest in imaging of the different parameters, which might characterize another physical properties of a tissue. The attenuation coefficient is one of such parameters and theoretically it can be estimated using frequency shift of the RF signal. The frequency shift results from dispersive character of the attenuation in tissue and is a function of attenuation along the propagate path. In this work authors use echo’s mean frequency as an imaging modality. The results of measurement of tissue phantom using 10 MHz linear array are presented. The preliminary results are encouraging being the first attempt towards mapping of the attenuation in tissue.

Keywords:
parametric visualization, mean frequency, attenuation estimation

Abstract:
Advances in modern technology increases requirements for nondestructive characterization of material and biological properties in the μm range. The acoustic microscope presented in this paper combines C-scan and B-scan modes. The data collected during single XY scan allow to present transversal and horizontal crosssections of the sample as well as real three-dimensional images of the sample interior. The system consist of several components: step motor driven mechanical scanner, transmitter/ receiver device, ADC 1 GHz board, ultrasonic heads, PC-class computer and image processing and visualization software. Image processing software is used for initial 3D image analysis of the whole image or its fragments, and for preparing it this way for vectorization. To achieve vectorization we used VTK (Visualization Tool Kit) library from Kitware Inc., which is the open source software, designed for 3D graphics and image processing. Finally iso-surface is constructed and presented as 3D scene in interactive GUI (Graphical User Interface).

Keywords:
3D visualization, microscope, ultrasound

Abstract:
The maximization of penetration depth with concurrent retaining or enhancement of image resolution constitutes one of the time invariant challenges in ultrasound imaging. To solve this problem a pulse compression technique employing long coded sequences is now under intensive investigation and in fact some of the corresponding techniques were already implemented in commercial scanning machines. This paper investigates the influence of the effective bandwidth of the transducer on the behaviour of the encoding/compression technique and its potential influence on the axial resolution. We have investigated two different bits lengths – one and two periods – in the Golay sequences resulting in substantial difference of the bandwidth of the transmitted sequences. Three transducers with different fractional bandwidths were used in the experiments: 6 MHz focused transducer with 25% fractional bandwidth, 4.4 MHz flat transducer with 58% fractional bandwidth and 6 MHz flat, composite transducer with 80% fractional bandwidth. The experimental results are clearly showing that the elongation of the Golay single bit length (two cycles in our case) compensates for the limited transducer bandwidth. For 25% bandwidth peak-to-peak echo increased by 1.89 times; for 58% bandwidth peak-to-peak echo amplitude increased by 1.62 times, and for 80% bandwidth peak-to-peak echo increased by 1.47 times.

Keywords:
ultrasound imaging, transducer bandwidth, Golay complementary sequences

Keywords:
ultrasound exposure, therapcutic ultrasound, membraue pcrmeability, giant vesicles

Abstract:
A novel, free from paraxial approximation and computationally efficient numerical algorithm capable of predicting 4D acoustic fields in lossy and nonlinear media from arbitrary shaped sources (relevant to probes used in medical ultrasonic imaging and therapeutic systems) is described. The new WE (wave envelopes) approach to nonlinear propagation modeling is based on the solution of the second order nonlinear differential wave equation reported in [J. Wojcik, J. Acoust. Soc. Am. 104 (1998) 2654-2663; V.P. Kuznetsov, Akust. Zh. 16 (1970) 548-553]. An incremental stepping scheme allows for forward wave propagation. The operator-splitting method accounts independently for the effects of full diffraction, absorption and nonlinear interactions of harmonics. The WE method represents the propagating pulsed acoustic wave as a superposition of wavelet-like sinusoidal pulses with carrier frequencies being the harmonics of the boundary tone burst disturbance. The model is valid for lossy media, arbitrarily shaped plane and focused sources, accounts for the effects of diffraction and can be applied to continuous as well as to pulsed waves. Depending on the source geometry, level of nonlinearity and frequency bandwidth, in comparison with the conventional approach the Time-Averaged Wave Envelopes (TAWE) method shortens computational time of the full 4D nonlinear field calculation by at least an order of magnitude; thus, predictions of nonlinear beam propagation from complex sources (such as phased arrays) can be available within 30-60 min using only a standard PC. The approximateratio between the computational time costs obtained by using the TAWE method and the conventional approach in calculations of the nonlinear interactions is proportional to (1/N)**2, and in memory consumption to 1/N where N is the average bandwidth of the individual wavelets. Numerical computations comparing the spatial field distributions obtained by using both the TAWE method and the conventional approach (based on a Fourier series representation of the propagating wave) are given for circular source geometry, which represents the most challenging case from the computational time point of view. For two cases, short (2 cycle) and long (8 cycle) 2 MHz bursts, the computational times were 10 min and 15 min versus 2 h and 8 h for the TAWE method versus the conventional method, respectively.

Keywords:
Nonliear propagation, Envelope waves, Fast calculations

Abstract:
This work reports the results of measurements of spatial distributions of ultrasound fields obtained from five energizing schemes. Three different codes, namely, chirp signal and two sinusoidal sequences were investigated. The sequences were phase modulated with 13 bits Barker code and 16 bits Golay complementary codes. Moreover, two reference signals generated as two and sixteen cycle sine tone bursts were examined. Planar, 50% (fractional) bandwidth, 15 mm diameter source transducer operating at 2 MHz center frequency was used in all measurements. The experimental data were collected using computerized scanning system and recorded using wideband, PVDF membrane hydrophone (Sonora 804). The measured echoes were compressed, so the complete pressure field in the investigated location before and after compression could be compared. In addition to a priori anticipated increase in the signal to noise ratio (SNR) for the decoded pressure fields, the results indicated differences in the pressure amplitude levels, directivity patterns, and the axial distance at which the maximum pressure amplitude was recorded. It was found that the directivity patterns of non-compressed fields exhibited shapes similar to the patterns characteristic for sinusoidal excitation having relatively long time duration. In contrast, the patterns corresponding to compressed fields resembled those produced by brief, wideband pulses. This was particularly visible in the case of binary sequences. The location of the maximum pressure amplitude measured in the 2 MHz field shifted towards the source by 15 mm and 25 mm for Barker code and Golay code, respectively. The results of this work may be applicable in the development of new coded excitation schemes. They could also be helpful in optimizing the design of imaging transducers employed in ultrasound systems designed for coded excitation. Finally, they could shed additional light on the relationship between the spatial field distribution and achievable image quality and in this way facilitate optimization of the images obtained using coded systems.

Keywords:
coded excitation, sound fields

Abstract:
This study concerns the development and investigation of a new composing method of short coded sequences and their transmission based on well-known Golay complementary codes and applied compression technique allowing to increase the signal-to-noise ratio (SNR) and penetration. This new method can potentially play important role in examination of superficial structures, e.g. dermatology, ophthalmology, etc. This paper reports the results of examination of the two pairs 3.5 MHz coded sequences of the same duration: the single 32-bits pair Golay sequences and combined sequences consisting of two 16-bits Golay codes separated in time. The results clearly demonstrate the potential of the combined coded transmission obtaining the SNR = 22.6 dB that is 2.6 dB higher than for the traditional Golay sequences and it is in case when coded length is two times shorter. For obtaining the same SNR using traditional method the code length should be at least 64 bits long, resulting in the increased dead zone up to 1.4 cm.

Keywords:
Golay complementary sequences, double transmission, dead zone

Abstract:
Objective:
The goal of this work was to develop a clinically applicable method for non-invasive acoustic determination of hematocrit in vivo.

Methods:
The value of hematocrit (HCT) was determined initially in vitro from the pulse-echo measurements of acoustic attenuation. The testing was carried out using a laboratory setup with ultrasound transducer operating at 20 MHz and employing human blood samples at the temperature of 37C. The attenuation coefficient measurements in blood in vitro and in vivo were implemented using multi-gated (128-gates), 20 MHz pulse Doppler flow meter. The Doppler signal was recorded in the brachial artery. Both in vitro and in vivo HCT data were compared with those obtained using widely accepted, conventional centrifuge method.

Results:
The attenuation coefficient in vitro was determined from the measurements of 168 samples with hematocrit varying between 23.9 and 51.6%. Those experiments indicated that the coefficient increased linearly with hematocrit. The HCT value was obtained from the 20 MHz data using regression analysis. The attenuation (() was determined as a 42.14 + 1.02*HCT (Np/m). The corresponding standard deviation (SD), and the correlation coefficient were calculated as SD = 2.4 Np/m, and R = 0.9, (p<0.001), respectively The absolute accuracy of in vivo measurements in the brachial artery was determined to be within 5% HCT.

Conclusions:
The method proposed appears to be promising for in vivo determination of hematocrit as 5% error is adequate to monitor changes in patients in shock or during dialysis. It was found that the multigate system largely simplified the placement of an ultrasonic probing beam in the center of the blood vessel. Current work focuses on enhancing the method’s applicability to arbitrary selected vessels and reducing the HCT measurement error to well below 5%.

Keywords:
hematocrit, blood, Doppler, power Doppler, multigate Doppler

Abstract:
Coded ultrasonography is intensively studied in many laboratories due to its remarkable properties: increased depth penetration, signal-to-noise ratio (SNR) gain and improved axial resolution. However, no data concerning the spatial behavior of the pressure field generated by coded bursts transmissions were reported so far. Five different excitation schemes were investigated. Flat, circular transducer with 15 mm diameter, 2 MHz center frequency and 50% bandwidth was used. The experimental data was recorded using the PVDF membrane hydrophone and collected with computerized scanning system developed in our laboratory. The results of measured pressure fields before and after compression were then compared to those recorded using standard ultrasonographic short-pulse excitation. The increase in the SNR of the decoded pressure fields is observed. The modification of the spatial pressure field distribution, especially in the intensity and shape of the sidelobes is apparent. Coded sequences are relatively long and, intuitively, the beam shape could be expected to be very similar to the sound field of long-period sine burst. This is true for non-compressed distributions of examined signals. However, as will be shown, the compressed sound fields, especially for the measured binary sequences, are similar rather to field distributions of short, wideband bursts.

Keywords:
coded excitation, ultrasonic field distribution, pulse compression, matched filtration, medical imaging

Abstract:
The nonlinear pulsed acoustic pressure field from a focused square aperture is considered. Experimental measurements in water of a 4D sound field radiated from a 2.8 MHz focused square transducer of a 20 mm side and a 80 mm focal distance for excitation level producing an average acoustic pressure P0 = 0.14 MPa at its surface are presented. The obtained results are compared with the numerical calculation results for the same boundary conditions. The novel, free from paraxial approximation and computationally efficient numerical algorithm was used to simulate the 4D nonlinear pulsed pressure field from the nonaxisymmetric acoustic source. Our theoretical model was based on the Time-Averaged Pressure Envelope (TAPE) method recently developed that enable to represent the propagated pulsed disturbance as a superposition of sinusoidal wavelets with carrier frequencies being the harmonics of the initial tone burst and with envelopes determined by the TAPE method. The novel approach to the solution of the nonlinear wave equation enabled to simulate full 4D nonlinear field for given boundary conditions in a dozen or so minutes utilizing the computational power of the standard PC.

Keywords:
square spherically focused transducer, pulsed waves, nonlinear propagation in water, sound fields, numerical modelling

Abstract:
The influence of finite aperture and frequency response of piezoelectric ultrasonic hydrophone probes on the Thermal and Mechanical Indices was investigated using a comprehensive acoustic wave propagation model. The experimental verification of the model was obtained using a commercially available, 8 MHz, dynamically focused linear array and a single element, 5 MHz, focused rectangular source. The pressure–time waveforms were recorded using piezoelectric polymer hydrophone probes of different active element diameters and bandwidths. The nominal diameters of the probes ranged from 50 to 500 μm and their usable bandwidths varied between 55 and 100 MHz. The Pulse Intensity Integral (PII), used to calculate the Thermal Index (TI), was found to increase with increasing bandwidth and decreasing effective aperture of the probes. The Mechanical Index (MI), another safety indicator, was also affected, but to a lesser extent. The corrections needed were predicted using the model and successfully reduced the discrepancy as large as 30% in the determination of PII. The results of this work indicate that by accounting for hydrophones' finite aperture and correcting the value of PII, all intensities derived from the PII can be corrected for spatial averaging error. The results also point out that a caution should be exercised when comparing acoustic output data. In particular, hydrophone's frequency characteristics of the effective diameter and sensitivity are needed to correctly determine the MI, TI, and the total acoustic output power produced by an imaging transducer.

Keywords:
Ultrasound imaging, Nonlinear propagation, Spatial averaging, Safety indices

Abstract:
To facilitate the implementation and verification of the new ultrasound hydrophone calibration techniques described in the companion paper (somewhere in this issue) a nonlinear propagation model was developed. A brief outline of the theoretical considerations is presented and the model’s advantages and disadvantages are discussed. The results of simulations yielding spatial and temporal acoustic pressure amplitude are also presented and compared with those obtained using KZK and Field II models. Excellent agreement between all models is evidenced. The applicability of the model in discrete wideband calibration of hydrophones is documented in the companion paper somewhere in this volume.

Keywords:
Nonlinear propagation modeling, Nonlinear propagation, JW model

Abstract:
A number of ultrasound imaging systems employs harmonic imaging to optimize the trade off between resolution and penetration depth and center frequencies as high as 15 MHz are now used in clinical practice. However, currently available measurement tools are not fully adequate to characterize the acoustic output of such nonlinear systems primarily due to the limited knowledge of the frequency responses beyond 20 MHz of the available piezoelectric hydrophone probes. In addition, ultrasound hydrophone probes need to be calibrated to eight times the center frequency of the imaging transducer. Time delay spectrometry (TDS) is capable of providing transduction factor of the probes beyond 20 MHz, however its use is in practice limited to 40 MHz. This paper describes a novel approach termed time gating frequency analysis (TGFA) that provides the transduction factor of the hydrophone probes in the frequency domain and significantly extends the quasi-continuous calibration of the probes up to 60 MHz. The verification of the TGFA data was performed using TDS calibration technique (up to 40 MHz) and a nonlinear calibration method (up to 100 MHz). The nonlinear technique was based on a novel wave propagation model capable of predicting the true pressure–time waveforms at virtually any point in the field. The spatial averaging effects introduced by the finite aperture hydrophones were also accounted for. TGFA calibration results were obtained for different PVDF probes, including needle and membrane designs with nominal diameters from 50 to 500 μm. The results were compared with discrete calibration data obtained from an independent national laboratory and the overall uncertainty was determined to be ±1.5 dB in the frequency range 40–60 MHz and less than ±1 dB below 40 MHz.

Keywords:
Time gating frequency analysis (TGFA), Time delay spectrometry (TDS), High frequency hydrophone calibration, Nonlinear hydrophone calibration, High frequency ultrasound, Ultrasonic metrology

Abstract:
Anisotropy is inherently related to microstructural arrangement within a representative volume of material. The microstructure can be represented by a second order tensor whose eigenvectors specify the orientation of the axes of material symmetry. In this paper, failure criteria for geomaterials are formulated in terms of the stress state and a microstructure tensor. The classical criteria for isotropic materials are generalized for the case of orthotropy as well as transverse isotropy. The proposed approach is illustrated by a simple example demonstrating the sensitivity of the uniaxial strength of the material to the orientation of the sample relative to the loading direction.

Abstract:
An approximate solution for the streaming velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation, the solution of the Navier-Stokes equation for the axial components of the streaming velocity. The theoretical model was verified experimentally using a 32 MHz pulsed Doppler unit. The experimental acoustical fields were produced by three different 4 mm diameter flat and focused transducers driven by the transmitter generating the average acoustic power within the range from 1 microW to 6 mW. The streaming velocity was measured along the ultrasonic beam from 0 to 2 cm. Streaming was induced in a solution of water and corn starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water, changed from 0.3 to 40 grams of starch in 1 l of distilled water. For applied acoustic powers, the streaming velocity changed linearly from 0.2 to 40 mm/s. Both, the theoretical solutions for plane and focused waves and the experimental results were in good agreement. The streaming velocity field was also visualised using the particle image velocimetry (PIV) and two different evaluation methods. The first based on the FFT-based cross-correlation analysis between small sections for each pair of images and the second employing the algorithm of searching for local displacements between several images.

Abstract:
The pressure gradient along the ultrasonic beam results in medium streaming. Following Nyborg's analysis of the Navier-Stokes equation, Wu and Du developed an approximate solution for the streaming velocity generated by flat and weakly focused transducers. We have modified their solution of the Poisson equation by directly deriving the Dirichlet boundary conditions to be applied for this type of equation. Our numerical results (for the linear case) were about one half smaller for flat and weakly focused Gaussian beam transducers compared to the results by Wu and Du. The theoretical calculations were verified using a purpose-designed 32-MHz pulsed Doppler unit. The applied average acoustic power was changed from 1 μW to 6 mW, the burst width was 0.5 μs and the pulse repetition frequency was 32 kHz. The experiments were done on 4-mm-diameter flat and focused (focal distance = 8 and 12 mm) transducers. The streaming was measured along the ultrasonic beam from 0–20 mm; at all positions, the maximum Doppler frequency was estimated from the recorded spectra. Streaming was induced in a solution of water and corn starch. The experimental results showed that, for a given acoustic power, the streaming velocity was independent of the starch density in water changed from 0.3–40 g of starch in 1 l of distilled water. For applied acoustic powers, the streaming velocity changed linearly from 0.2–40 mm/s. Both the theoretical solutions for plane and focused waves and the experimental results were in good agreement.

Keywords:
Ultrasound, Streaming, Nonlinear ultrasound effects, Doppler

Abstract:
Examination of the carotid artery stenosis is very important in the diag-nosis of cerebrovascular diseases. New possibilities in the diagnosis of stenotic lesions are provided by ultrasonic Doppler angiography. The aim of this paper is to present a Doppler imaging system developed by the authors for the exami¬nation of blood flowing in carotid arteries. The system is based upon a 5 MHz bi-directional c.tv. Doppler flowmeter with a separate output for anterograde and retrograde flows. A special bank of filters converts signals into various levels of the gray-scale display which correspond to the value of the blood flow velocity. The ultrasonic probe is held by the scanning arm. The position of the probe on the skin of the patient is electronically sensed by the position-sensing circuity which causes the bright spot on the image display to move according to the position of the probe. The Doppler image from the artery is stored in a digital memory system. The clinical results obtained by means of this system showed good agreement with X-ray arteriography for obstructions occluding more than 50 per cent of the arterial diameter.

Abstract:
The authors present results of quantitative measurements of blood in vivo in the carotid artery of man. The Doppler pulse technique was used after being previously verified for steady state flows in tubes and for pulsating flows in a canine aorta where the electromagnetic method was also used for comparison.

An ultrasonic probe with two transducers was adapted for determination of the angle of the ultrasonic beam in relation to the vessel allowing the measurement of the vessel diameter which was also determined by means of the ultrasonographic B-mode technique.

By means of the Doppler pulse method profiles of the blood velocity in the carotid artery were determined as a function of time.

The continous wave Doppler technique together with the zero-crossing system and spectral analysis were also used for making measurements.

The flow velocity and the shape of the flow curve with time obtained with the above techniques showed good agreement. The measured flow rate in the carotid artery amounted to QM = 1.61/min (maximum instantaneous value) and Q0 - 0.531/min (mean time value).

Abstract:
Convolutional neural networks (CNNs) have achieved remarkable success in medical image analysis tasks. In ultrasound (US) imaging, CNNs have been applied to object classification, image reconstruction and tissue characterization. However, CNNs can be vulnerable to adversarial attacks, even small perturbations applied to input data may significantly affect model performance and result in wrong output. In this work, we devise a novel adversarial attack, specific to ultrasound (US) imaging. US images are reconstructed based on radio-frequency signals. Since the appearance of US images depends on the applied image reconstruction method, we explore the possibility of fooling deep learning model by perturbing US B-mode image reconstruction method. We apply zeroth order optimization to find small perturbations of image reconstruction parameters, related to attenuation compensation and amplitude compression, which can result in wrong output. We illustrate our approach using a deep learning model developed for fatty liver disease diagnosis, where the proposed adversarial attack achieved success rate of 48%.

Keywords:
adversarial attacks, deep learning, fatty liver, transfer learning, ultrasound imaging

Abstract:
Precise quantitative analysis of the sonothrombolysis process is required to minimise the amount of thrombolytic drug dangerous for the patient, because it can cause internal hemorrhage. Verification of the effects of other drugs or other procedures for the elimination of thrombi, for example ultrasound contrast microbubbles, also requires quantitative research. For microscopic examination of the thrombolysis process, the Rexolite parallel plate flow chamber has been used. The internal dimensions of the chamber were 11x1x20 mm. In order to eliminate the standing wave, the incident wave was perpendicular to the reflected one. The narrowband chirp driven transducer suppressed the surface waves in Rexolite. The clot dissolution was processed at 40 kHz – 6 MHz ultrasound frequencies and 2 W/cm2 spatial averaged, temporal averaged intensities. The thrombus was obtained from a 5 μl drop of blood placed directly inside a flow chamber. The flow chamber was filled with the cell culture medium Dulbecco's modified Eagle's medium. The flow in the chamber was forced by a peristaltic pump at a speed of 3.8 ml/min. The Actilyse tissue plasminogen activator at a concentration of 10 μg/ml was added. The similarity of the thrombolysis process obtained from 5 μl of blood with a similar volume fragment cut from a larger thrombus was experimentally verified. Thrombus volume was estimated from microscopic photographs by calculating its surface area and its optical transparency. At 2 W/cm2 ultrasound intensity, took the thrombus 4, 8, 9 and 12 minutes to completely dissolve for the centre ultrasound frequencies of 40.9, 149, 209 kHz and 1.02 MHz, respectively. For higher frequencies, the thrombus only reduced its volume by 82%, 69% and 27% for the frequencies 2.10, 3.34 and 6.63 MHz, respectively. Sonication for 20 - 60 minutes did not cause further dissolution of thrombi.

Keywords:
ultrasound, blood, thrombus, thrombolysis, parallel plate flow chamber

Abstract:
In this work we investigate the usefulness and robustness of transfer learning with deep convolutional neural networks (CNNs) for breast lesion classification in ultrasound (US). Deep learning models can be vulnerable to adversarial examples, engineered input image pixel intensities perturbations that force models to make classification errors. In US imaging, distribution of US image pixel intensities relies on applied US image reconstruction algorithm. We explore the possibility of fooling deep learning models for breast mass classification by modifying US image reconstruction method. Raw radio-frequency US signals acquired from malignant and benign breast masses were used to reconstruct US images, and develop classifiers using transfer learning with the VGG19, InceptionV3 and InceptionResNetV2 CNNs. The areas under the receiver operating characteristic curve (AUCs) obtained for each deep learning model developed and evaluated using US images reconstructed in the same way were equal to approximately 0.85, and there were no associated differences in AUC values between the models (DeLong test p-values > 0.15). However, due to small modifications of the US image reconstruction method the AUC values for the models utilizing the VGG19, InceptionV3 and InceptionResNetV2 CNNs significantly decreased to 0.592, 0.584 and 0.687, respectively. Our study shows that the modification of US image reconstruction algorithm can have significant negative impact on classification performance of deep models. Taking into account medical image reconstruction algorithms may help develop more robust deep learning computer aided diagnosis systems.

Keywords:
Adversarial attacks, Breast lesion classification, Computer aided diagnosis, Deep learning, Robustness, Ultrasound imaging, Transfer learning

Abstract:
Under the influence of pathological changes, the blood coagulates inside the blood vessel, creating a thrombus. The thrombus dissolution process is called thrombolysis. The aim of the study is to evaluate the thrombolysis process by the interaction of the thrombolitic drug and ultrasound. The clot dissolution process was analyzed in a specially designed, transparent for ultrasound parallel plate flow chamber. Inside, a freshly coagulated human blood sample was exposed to ultrasound. A liquid containing the tissue plasminogen activator drug in a concentration of 10 μg/ml passed around the sample. The liquid flow was forced by a peristaltic pump. The source of ultrasound was a 1 MHz flat ultrasonic transducer with a 25 mm diameter. The transducer radiated a 1000 periods burst, repeated every 2500 periods and space averaged time averaged intensities of 0.2-1.6 W/cm2. The efficacy of thrombus dissolution was observed by means of a designed parallel plate flow chamber and the time of thrombus complete dissolution was measured. The best result for the 1 MHz frequency and space averaged time averaged intensity of 1.6 W/cm2 was recorded, where the thrombus was dissolved within 5.5 minutes.

Keywords:
ultrasound, blood, thrombus, thrombolysis, parallel plate flow chamber

Abstract:
The article attempts to select an ultrasound system to assess of endothelium dysfunction-dependent flow mediated dilation (FMD) and shear rate (SR) in radial artery after several minutes of hyperaemia. Methods: We compare the effective axial resolution and Doppler sensitivity of the standard US working below 12 MHz and high frequency (close to 20 MHz) scanning systems measuring the vessel diameter and blood flow measurements in radial arteries. FMD and FMD and SR were measured in Control group of 14 healthy volunteers, and in 13 with stable coronary artery diseases (CAD). Results: In a laboratory experiment of imaging two closely spaced food plastic foils, over three times better axial resolution was demonstrated for the 20 MHz ultrasound system in which the resolution was close to 0.1 mm. Also the sensitivity of the external single 20 MHz pulse Doppler transducer proved to be over 20 dB better (in terms of signalto-noise ratio) than the pulse Doppler incorporated into the L14-5 linear array. FMD in Control group was in the range of 8÷16% with mean±sd equal to 12.13 ± 2.34%; in CAD group FMD was in the range of 0.1÷7 % with mean±sd equal to 3.01±2.18% which was significantly less. FMD/SR was equal to 3.08 ± 1.34 × 10–4 in Control group and 1.01 ± 0.76 × 10–4 in CAD group with ranges equal to 1.66 ÷ 7.8× 10–4 and 0.4 ÷ 2.4× 10–4, respectively. Conclusions: Increasing scanning and Doppler mode frequency to 20 MHz improved the precision of FMD and SR measurements. Statistically significant differences between the two groups were confirmed by statistical tests for FMD and FMD/SR with p-values < 0.05. The results obtained suggest the usefulness of the proposed ultrasonic system for measurements of FMD and SR in the radial artery to differentiate normal subjects from those with CAD.

Keywords:
radial artery, shear rate, reactive hyperaemia, endothelium, pulsed Doppler

Abstract:
Parallel plate flow chambers are widely used for cell research in conditions of constant or pulsatile liquid flow. They are also used to analyze the formation of thrombi. The authors designed a flow chamber that is transparent to ultrasound, thus enabling the microscopic observation of the thrombus dissolution process by interaction of drug, microbubbles and ultrasound in real time, in-vitro. Sonothrombolysis was performed at 1 MHz and 3.3 MHz ultrasound frequencies, at space-averaged and time-averaged intensities ISATA of 0.2 – 1.6 W/cm2. 1 mm thick slices of the human blood clots were exposed to ultrasound in the presence of the Actilyse tissue plasminogen activator at a concentration of 10 μg/ml flowing around the sample. Next, the effect of SonoVue microbubbles at a concentration of 5x105/ml on the dissolution of the thrombus was investigated. Thrombus size changes were observed under a 4x magnification microscope and were recorded as a function of time. The best result was achieved for the Actilyse tissue plasminogen activator at the 1 MHz and 1.6 W/cm2 ISATA, the thrombus was sonolysed within 5.5 minutes. The noticeable effect of the SonoVue microbubbles on the thrombolysis process appeared at 3.3 MHz, the thrombus was sonolysed in 12 min at ISATA = 1.6 W/cm2.

Keywords:
ultrasound, blood, thrombus, thrombolysis, parallel plate flow chamber

Abstract:
Streaming velocity mainly depends on the intensity and absorption of ultrasound in the media. For high frequencies exceeding 20 MHz the speed of streaming in blood is also affected by scattering effects on the blood cells and contrast agent microbubbles. According to theoretical calculations, 12.2 % increase in streaming velocity for 1 g/l starch concentration rise should be expected. The theory has also shown the reduction of the streaming velocity by low-density scatterers, estimated decrease was -9.7 % for BR14 contrast agent. The experimental measurements of streaming velocities were done in blood mimicking fluid and Bracco BR14 microbubbles dissolved in water. The streaming was generated by a plane 20 MHz ultrasonic transducer driven by a pulsed Doppler flowmeter. For starch concentration changing from 0.01g/l (reference fluid) up to 1g/l the streaming velocity increased by 13%, very close to the theoretical prediction. For BR14, the measured velocity was 9% less than in reference fluid and remained independent on the microbubbles concentration.

Keywords:
streaming, radiation force, starch, contrast agent, blood

Abstract:
In this paper we investigate how to assess the ultrasound nonlinearity coefficient using plane wave imaging. We employ the technique based on excitation of the medium with ultrasonic pulses of increasing amplitude level. As the pulse pressure is increased, due to medium nonlinearity, higher fraction of energy is transferred from the fundamental to higher harmonics during the propagation. In this case the amplitude of the backscattered echo is not linear in respect to the initial pulse amplitude at source. This phenomenon can be used for the nonlinearity coefficient assessment and show its implementation for the plane wave imaging. The method was validated experimentally using a wire phantom immersed in water and scanned using the Verasonics scanner. We discuss the usefulness of the proposed technique and its shortcomings. In comparison to other nonlinearity coefficient assessment methods, the presented technique works in the pulse-echo mode and it doesn't require information on second harmonic or using a special wide-band transducer. The method can be implemented directly into a medical scanner.

Keywords:
Plane wave imaging, nonlinear ultrasound, quantitative ultrasound, coefficient of nonlinearity

Abstract:
In this paper we propose a computer-aided diagnosis system for the breast lesion classification. Our approach is based on quantitative ultrasound and deep learning. We used the Nakagami imaging to create parametric maps of breast lesions that illustrate tissue scattering properties. For this task the sliding window technique was applied. The Nakagami parameter was calculated using the maximum likelihood estimator. Next, we used the Nakagami parameter maps to train a convolutional neural network. Classification performance was evaluated by 5-fold cross-validation. We obtained the area under the receiver operating characteristic curve equal to 0.91. The results showed that our approach is useful to distinguishing between malignant and benign breast lesions. The proposed method serves as a general approach for tissue characterization and differentiation. The Nakagami parameter used in this study can be replaced with other QUS parameters and the neural network can be trained in a similar fashion.

Keywords:
Nakagami imaging, quantitative ultrasound, convolutional neural networks, breast lesion classification, deep learning

Abstract:
A novel high-frequency scanning system, with a 20-MHz linear array transducer combined with 20-MHz pulsed Doppler, was introduced to evaluate the degree of radial artery flow-mediated dilation (FMD) and shear rate (SR)-normalized FMD (FMD/SR) after 5 min of reactive hyperaemia. In group I, comprising 27 healthy volunteers, FMD was 15 ± 4.8%, and in group II, comprising 17 patients with coronary artery disease, FMD was significantly smaller, being equal to 4.6 ± 4%. FMD/SR was equal to 5.365 ± 4.835·10-4 in group I and 1.3 ± 0.89·10-4 in group II. Statistically significant differences between the two groups were confirmed by Wilcoxon-Mann-Whitney test for FMD and FMD/SR (p-values < 0.01). AUCs of ROC curves for FMD and FMD/SR were greater than 0.9. The results confirm the usefulness of the proposed measurements of radial artery FMD and SR in differentiation of normal subjects from those with atherosclerotic lesions.

Keywords:
flow mediated vasodilation, radial artery, shear rate, reactive hyporaemia, endothelium, pulsed Doppler, ultrasonography.

Abstract:
Preceding atherosclerosis is endothelial dysfunction. There is therefore interest in the application of non-invasive clinical tools to assess endothelial function. There are commercially available ultrasound scanners to estimate Brachial Artery Reactive Response BARR by measuring the flow-mediated vasodilatation (FMD) of the brachial artery using 10–12 MHz linear array probes; however the precision in estimating of artery dilation does not exceeds 0.2 mm, far beyond the required one. We have introduced a high frequency scanning schemes; 25–35 MHz encoded (Golay) wobbling type imaging with- out Doppler (uScan developed in our lab, thick film wide bandwidth transducer, 50 microns axial resolution). In the second approach we have used 20 MHz linear scanning with 20 MHz pulsed Doppler attached to the linear array. Instead of brachial artery we have examined the radial artery where Radial Artery Reactive Response RARR was measured. The radial artery FMD were normalized using AUC of shear rate at the radial artery wall. The precision of the radial artery diameter measurements is over two times better using 20 MHz US instead of 7.5 MHz used for brachial artery FMD. The measured initial internal radial artery diameter was in range of 1.59–2.35 mm, the maximum diameter 2.01–2.60 mm was observed 40 to 55 seconds after releasing the cuff. In a limited number (14) of examined young, healthy patients the FMDSR were in the range from 7.8
to 9.9 in arbitrary units. In older patients with minor cardiac history the normalized FMDSR was clearly lower, 6.8 to 7.6.

Keywords:
thick film transducers, atherosclerosis, flow mediated vasodilation.

Abstract:
The aim of the study was finding the relationship between BIRADS classification combined with envelope K and Nakagami statistics of the echoes backscattered in the breast tissue in vivo and the histological data. 107 breast lesions were examined. Both, the RF echo-signal and B-mode images from the lesions and surrounding tissue were recorded. The analysis method was based on the combining data from BIRADS classifications and both distributions parameters. 107 breasts lesions - 32 malignant and 75 benign - were examined. When only BIRADS classification was used all malignant lesions were diagnosed correctly, however 34 benign lesions were sent for the biopsy unnecessarily. For K distribution the sensitivity and specificity were 78.13%, and 86.67% while for Nakagami statistics the sensitivity and specificity were 62.50% and 93.33%, respectively. Combined K and BIRADS resulted in sensitivity of 96.67% and specificity 60%. Combined BIRADS (3/4a cut-off) plus Nakagami statistics showed 100% of sensitivity with specificity equal 57.33%, decreasing the number of lesions which were biopsied from 34 to 28.

Keywords:
breast cancer, quantitative ultrasound, BIRADS

Abstract:
Nakagami distribution is used to model the statistical properties of backscattered echoes in tissue. The proper estimate requires the compensation of attenuation along each scanning line. Attenuation of the wave results in decreasing of the envelope mean intensity with depth what modifies the Nakagami scale parameter. This phenomenon violates the assumption that envelope samples within region of interest are identically distributed and disrupts estimation. Here, we investigate the influence of wave attenuation on Nakagami shape parameter estimators for various scattering scenarios, attenuation coefficients and region of interest size. Three methods are proposed to solve this issue. Scans of a thyroid and of a breast lesion are analyzed. It was found that proposed methods improved the estimation, especially when larger regions were used to collect envelope samples.

Keywords:
ultrasound, breast cancer, Nakagami distribution

Abstract:
Preceding atherosclerosis is endothelial dysfunction. There is therefore interest in the application of non-invasive clinical tools to assess endothelial function. There are commercially available ultrasound scanners to measure flow-mediated vasodilatation (FMD) of the brachial artery using 10-12 MHz linear array probes, however the attainable precision in estimating the changes in artery dilation does not exceeds 0.2 mm, far beyond the required one. We have introduced a high frequency scanning schemes 25-35MHz encoded (Golay) wobbling type imaging without Doppler (uScan developed in our lab, thick film wide bandwidth transducer, 50 microns axial resolution) and 20 MHz ultrasound (Ultrasonix) with 20 MHz pulsed Doppler attached to the linear array. The FMD results were normalized using AUC of shear rate at the radial artery wall.

Keywords:
thick-film transducers, flow-mediated vasolidation, radial artery, shear rate

Abstract:
Nowadays there are new modalities in ultrasound imaging allowing better characterization of tissue regions with different stiffness. We are proposing an approach based on simultaneous propagation of two waves being a combination of two pulses differing in pressure and frequency: a low frequency pulse is expected to change the local scattering properties of the tissue due to compression/rarefaction while a high frequency pulse is used for imaging. Two transmissions are performed for each scanning line. First, with the imaging pulse that propagates on maximum compression caused by a low frequency wave. Next, the low frequency wave is inverted and the imaging pulse propagates over the maximum rarefaction. After the processing of the subtracted echoes from subsequent transmissions including wavelet transform and band-pass filtering, differential images were reconstructed. The low frequency wave has a visible impact on the scattering properties of the tissue which can be observed on a differential image.