Staff

Abstract:
Recently, magneto-ultrasound heating of tissue in the presence of magnetic nanoparticles (NPs) has been studied due to its high potential for use in oncological hyperthermia. It has been published that a synergistic effect, generation of additional heat caused by magneto-ultrasonic coupling, was observed in a tissue-mimicking material (TMM) enriched with magnetic NPs. The specific absorption rate (SAR) was determined from the temperature rise measurements in a focus of the ultrasound beam. It is important to use precise measurement methods when considering medical applications, for which there are limitations to the power of each field, resulting from the prevention of biological phenomena dangerous to the patient. This study demonstrates that in magneto-ultrasonic heating SAR can be measured much more accurately if the ultrasonic field is almost uniform. Measurements were performed on TMM containing Fe3O4 NPs with a diameter of approximately 8 nm and superparamagnetic properties. Both, the measurement and simulation results showed that the errors resulting from the inaccuracy of placing the temperature probe are smaller than in the case of the focused ultrasound. At the same time, the temperature increase caused by the ultrasonic field is almost linear and the influence of heat convection on the SAR determination is negligible. The measurements showed that magneto-ultrasonic hyperthermia can provide the desired thermal effect at lower ultrasound powers and magnetic fields compared to ultrasonic or magnetic hyperthermia used alone. No synergy effect was recorded.

Keywords:
Magnetic nanoparticle-mediated hyperthermia,Dual-mode ultrasonic-magnetic hyperthermia,Specific absorption rate,Hyperthermia efficiency

Abstract:
High Intensity Focused Ultrasound (HIFU) is used in clinical practice for thermal ablation of malignant and benign solid tumors located in various organs. One of the reason limiting the wider use of this technology is the long treatment time resulting from i.a. the large difference between the size of the focal volume of the heating beam and the size of the tumor. Therefore, the treatment of large tumors requires scanning their volume with a sequence of single heating beams, the focus of which is moved in the focal plane along a specific trajectory with specific time and distance interval between sonications. To avoid an undesirable increase in the temperature of healthy tissues surrounding the tumor during scanning, the acoustic power and exposure time of each HIFU beam as well as the time intervals between sonications should be selected in such a way as to cover the entire volume of the tumor with necrosis as quickly as possible. This would reduce the costs of treatment. The aim of this study was to quantitatively evaluate the hypothesis that selecting the average acoustic power and exposure time for each individual heating beam, as well as the temporal intervals between sonications, can significantly shorten treatment time. Using 3D numerical simulations, the dependence of the duration of treatment of a tumor with a diameter of 5 mm or 9 mm (requiring multiple exposure to the HIFU beam) on the sonication parameters (acoustic power, exposure time) of each single beam capable of delivering the threshold thermal dose (CEM43 = 240 min) to the treated tissue volume was examined. The treatment duration was determined as the sum of exposure times to individual beams and time intervals between sonications. The tumor was located inside the ex vivo tissue sample at a depth of 12.6 mm. The thickness of the water layer between the HIFU transducer and the tissue was 50 mm. The sonication and scanning parameters selected using the developed algorithm shortened the duration of the ablation procedure by almost 14 times for a 5-mm tumor and 20 times for a 9-mm tumor compared to the duration of the same ablation plan when a HIFU beam was used of a constant acoustic power, constant exposure time (3 s) and constant long time intervals (120 s) between sonications. Results of calculations of the location and size of the necrotic lesion formed were experimentally verified on ex vivo pork loin samples, showing good agreement between them. In this way, it was proven that the proper selection of sonication and scanning parameters for each HIFU beam allows to significantly shorten the time of HIFU therapy.

Keywords:
HIFU ablation planning,HIFU therapy duration shortening,Tissue ex vivo,k-wave model,Experimental verification of therapy accuracy,Numerical simulation

Abstract:
Nanofibrous materials generated through electrospinning have gained significant attention in tissue regeneration, particularly in the domain of bone reconstruction. There is high interest in designing a material resembling bone tissue, and many scientists are trying to create materials applicable to bone tissue engineering with piezoelectricity similar to bone. One of the prospective candidates is highly piezoelectric poly(vinylidene fluoride) (PVDF), which was used for fibrous scaffold formation by electrospinning. In this study, we focused on the effect of PVDF molecular weight (180,000 g/mol and 530,000 g/mol) and process parameters, such as the rotational speed of the collector, applied voltage, and solution flow rate on the properties of the final scaffold. Fourier Transform Infrared Spectroscopy allows for determining the effect of molecular weight and processing parameters on the content of the electroactive phases. It can be concluded that the higher molecular weight of the PVDF and higher collector rotational speed increase nanofibers’ diameter, electroactive phase content, and piezoelectric coefficient. Various electrospinning parameters showed changes in electroactive phase content with the maximum at the applied voltage of 22 kV and flow rate of 0.8 mL/h. Moreover, the cytocompatibility of the scaffolds was confirmed in the culture of human adipose-derived stromal cells with known potential for osteogenic differentiation. Based on the results obtained, it can be concluded that PVDF scaffolds may be taken into account as a tool in bone tissue engineering and are worth further investigation.

Keywords:
scaffolds,polymers,piezoelectricity,bone tissue engineering,nanofibers,regenerative medicine

Abstract:
Magnetic nanoparticles (MNP)s of Fe3O4 were synthesized in the co-precipitation reaction of iron chlorides dissolved in water and ammonia water. To produce polyethylene glycol (PEG) coatings of the NMPs, we added PEG to the ammonia water during the fabrication process. Magnetic fluids, ferrofluids, for research were prepared as oleic acid suspension of bare and PEG-coated nanoparticles at four concentrations. The results of the conducted calorimetric experiments confirmed that the efficiency of heating ferrofluids strongly depends on the concentration of nanoparticles in fluids. The results also indicate that the ferrofluids containing PEG-coated NPs heat up more than ferrofluids with bare nanoparticles. They are characterized by a higher specific absorption rate (SAR) value calculated from the initial slope of temperature versus time curve during heating. 10.1016/j.jmmm.2021.168918, 10.1016/j.jmmm.2022.169422

Keywords:
nanoparticle fluid hyperthermia, magnetite nanoparticles, PEG-coated nanoparticles, hyperthermia

Abstract:
We studied sonochemical reactions resulting from ultrasonic treatment of potassium hexacyanoferrate(II) in aqueous solutions using a custom-built apparatus working at 536 kHz. We concluded that primary reactions are completely dominated by oxidation of Fe(II) to Fe(III) and did not find any evidences for degradation of cyanide. At the highest concentration used in the present study (0.1 M) we detected formation of pentacyanoaquaferrate(II) complex, which is most probably formed in reactions between hexacyanoferrate(III) anions and hydrogen atoms or hydrated electrons formed in sonochemical processes. We also determined that hydroxyl radicals formation rate in our system, (8.7 ± 1.5)∙10^-8 M∙s^-1, is relatively high compared to other reported experiments. We attribute this to focusing of the ultrasonic wave in the sample vessel. Finally, we suggest that oxidation rate of hexacyanoferrate(II) anions can be a convenient benchmark of efficiency of sonochemical reactors.

Keywords:
sonochemistry,sonooxidation,sonoreactor,advanced oxidation processes,waste-water treatment

Abstract:
Polyvinylidene fluoride (PVDF) is one of the most important piezoelectric polymers. Piezoelectricity in PVDF appears in polar β and ɣ phases. Piezoelectric fibers obtained by means of electrospinning may be used in tissue engineering (TE) as a smart analogue of the natural extracellular matrix (ECM). We present results showing the effect of rotational speed of the collecting drum on morphology, phase content and in vitro biological properties of PVDF nonwovens. Morphology and phase composition were analyzed using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), respectively. It was shown that increasing rotational speed of the collector leads to an increase in fiber orientation, reduction in fiber diameter and considerable increase of polar phase content, both b and g. In vitro cell culture experiments, carried out with the use of ultrasounds in order to generate electrical potential via piezoelectricity, indicate a positive effect of polar phases on fibroblasts. Our preliminary results demonstrate that piezoelectric PVDF scaffolds are promising materials for tissue engineering applications, particularly for neural tissue regeneration, where the electric potential is crucial.

Keywords:
scaffolds, electrospinning, polyvinylidene fluoride, tissue engineering

Abstract:
The purpose of this work is to present a theoretical analysis of top orthogonal to bottom arrays of conducting electrodes of infinitesimal thickness (conducting strips) residing on the opposite surfaces of piezoelectric slab. The components of electric field are expanded into double periodic Bloch series with corresponding amplitudes represented by Legendre polynomials, in the proposed semi-analytical model of the considered two-dimensional (2D) array of strips. The boundary and Edge conditions are satisfied directly by field representation, as a result. The method results in a small system of linear equations for unknown expansion coefficients to be solved numerically. A simple numerical example is given to illustrate the method. Also a test transducer was designed and a pilot experiment was carried out to illustrate the acoustic-wave generating capabilities of the proposed arrangement of top orthogonal to bottom arrays of conducting strips.

Keywords:
boundary value problem, Fourier series, Bloch series, partial differential equations, piezoelectric transducer

Abstract:
Purpose: Nowadays, the improvement of ultrasonic hyperthermia therapy is often achieved by adding hard particles to the sonicated medium in order to increase the heating efficiency. The explanation of the phenomenon of ultrasonic heating still requires testing on tissue mimicking materials (TMMs), enriched with particles of different sizes and physical properties. Our goal was to determine, by comparing their quantitative acoustic properties, which TMMs, with magnetic micro- or nanoparticles, convert more ultrasonic energy into heat or which of the particles embedded in the agar gel act as more effective thermal sonosensitizers. Methods: We manufactured a pure agar gel and an agar gel with the addition of magnetic micro- or nanoparticles in two proportions of 8 and 16 mg/ml. Ultrasound quantitative techniques, the broadband reflection substitution technique and backscattered spectrum analysis were used to characterize the samples by speed of sound (SOS), frequency-dependent attenuation, and backscattering coefficients. The integrated backscattering coefficients were also calculated. The quantitative parameters, scattering, and attenuation coefficients of ultrasound in phantoms with micro- and nanoparticles were estimated. Based on the attenuation and scattering of ultrasound in the samples, the ultrasonic energy absorption, which determines the heating efficiency, was evaluated. Additionally, the temperature increase during sonication of the phantoms by an ultrasonic beam was directly measured using thermocouples. Results: The density of the materials with nanoparticles was higher than for the materials with microparticles with the same fractions of particles. The SOS for all materials ranged from 1489 to 1499 m/s. The attenuation in the whole frequency range (3–8 MHz) was higher for the materials with nanoparticles than for the materials with microparticles. For the materials with the lower content (8 mg/ml) of particles, the attenuation coefficient was 0.2 dB/(MHz cm). For the 16 mg/ml concentration of nanoparticles and microparticles, the attenuation coefficients were 0.66 and 0.45 dB/(MHz cm), resectively. The value of backscattering coefficient in the whole frequency range was greater for the materials with microparticles than for the materials with nanoparticles. The values of the integrated backscattering coefficient were 0.05 and 0.08 1/m for the materials with nanoparticles and 0.46 and 0.82 1/m for the materials with microparticles and concentrations of 8 and 16 mg/ml, respectively. The rates of temperature increase in the first 3 s due to ultrasonic heating were higher for the materials with nanoparticles than for the materials with microparticles. Conclusions: Based on acoustical measurements, we confirmed that all materials can be used as tissue phantoms in the study of ultrasonic hyperthermia, as their properties were in the range of soft tissue properties. We found that the nanoparticle-doped materials had greater attenuation and smaller scattering of ultrasound than the materials with microparticles, so absorption in these materials is greater. Thus, the TMMs with nanoparticles convert more acoustic energy into heat and we conclude that magnetic nanoparticles are more effective thermal sonosensitizers than microparticles. This conclusion is confirmed by direct measurement of the temperature increase in the samples subjected to sonification.

Keywords:
backscattering coefficient, frequency-dependent attenuation, hyperthermia TMM, magnetic particles, ultrasound absorption

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:
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:
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:
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:
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 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

Abstract:
The study was aimed at elaboration of a mathematical model to describe the process of acoustic wave propagation in an inhomogeneous and absorbing medium, whereas the wave is generated by an ultrasonic probe. The modelling proces covered the phenomenon of ultrasonic wave backscattering on an elastic pipe with dimensions similar to the artery section. Later on the numerical codes were determined in order to calculate the fields of ultrasonic waves, as well as backscattered fields for various boundary conditions. Numerical calculations make it possible to definethe waveforms for electric signals that are produced when ultrasonic waves, being reflected and backsvattered by an artery model, are then received by the ultrasonic probe. It is the signalwhich pretty well corresponds with the actual RF signal that is obtained during measurements at the output of anultrasonic apparatus.

Keywords:
ultrasound, backscattering, artery, numerical model

Abstract:
Nonlinear propagation effects produced by focused pulses in blood were measured over a 20-cm range, being inspired by diagnostic applications in cardiology. The initial and maximum pressures applied during measurements in blood were equal to 0.40 MPapp and 0.76 MPapp, while the pressure estimated at the patient body surface equalled 0.70 MPapp. Measurements of the frequency characteristic and the linearity of the ultrasonic probe used in experiments were performed in water. A numerical procedure developed previously was applied in blood to calculate the pressure distribution of its first and second harmonics along the beam axis. The comparison of numerical and measured distributions in blood at a temperature of 37°C showed rather good agreement. Using numerical methods, a proportional growth of the second harmonic with the increased applied initial pressure was first observed, and finally the maximum limiting effect was found. In this way, much higher level of harmonics could be obtained. However, there arise the questions of the transmitting system construction and of the nonuniform resolution in the case of harmonic imaging when increasing the applied initial pressure.

Keywords:
Ultrasound, Pulses, Nonlinear propagation, Blood, Cardiology

Abstract:
Measurements in the very near field of piezoelectric transducers are fundamental for many ultrasonic problems. In such cases also the transducer vibrations should be known to perform mathematical models of radiated beams. Acoustic pressure measurements near to the transducer surface can give the necessary information. The pressure of the radiated wave at the transducer surface corresponds to its normal vibration velocity multiplied by the [ampersand]rho;c value of the medium. However, this is valid only for the central wave, when the edge wave of the transducer can be ignored. On the other hand, pressure measurements on and very near to the transducer surface are not possible because of the voltage leakage between the electronic transmitter and the PVDF hydrophone used in such measurements. By means of a numerical model, central and edge waves were found for a plane PZT transducer 7.5mm in radius, with the applied 2.7MHz voltage pulse composed of 3 cycles. Two types of boundary conditions of Dirichlet and Neumann were considered showing a negligible difference in the case of short pulses. Basing on numerical and experimental results, practical conditions were determined which make it possible to carry out pressure measurements in the very near field of the transducer, and hence to determine the transducer vibrations which are important for modeling ultrasonic pulse beams.

Abstract:
The effect of nonlinear propagation in fluid followed by soft tissue was studied both theoretically and experimentally for a most crucial case in obstetrical ultrasonography. For this purpose, short pressure pulses, with the duration time of 1.3 μs and a carrier frequency of 3 MHz, radiated by a concave transducer into water, with maximum intensities up to the value of 18 W/cm2, were computed and measured. The ultrasonic beam had the physical focus at the distance of 6.5 cm, where the highest focal intensity of ISPPA= 242 W/cm2 was obtained. In front of the transducer, at a distance of 7 cm, artificial tissue samples prepared on the basis of ground porcine kidney, with a thickness of 0.5, 1.5 and 3 cm, were placed in water. Pressure pulses and their spectral components were produced numerically and measured by means of a PVDF hydrophone in water before and after penetrating the tissue samples. The theoretical analysis and measurements were carried out, in every case, for two signal levels: for a high level assuring nonlinear propagation and for a low one where conditions of linear propagation were fulfilled. In this way, it was possible to compare directly the effects of nonlinear and linear propagation, in every case showing a good conformity of theoretical values with measured ones. A method of determination of the effective frequency response of the hydrophone was elaborated to enable quantitative comparisons of numerical and experimental results. The theoretical part of our study was based on a paper of Wójcik (1998), enabling us to compute the characteristic function of nonlinear increase of absorption. An agreement of up to 10% was obtained when comparing theoretical and measured values of these functions in the investigated beam in water and behind tissue samples. The results obtained showed that the recently given theory of nonlinear absorption, based on the spectral analysis and the elaborated numerical procedures, may be useful in various practical ultrasonic medical problems and also in technological applications.

Keywords:
Ultrasound, Pulses, Nonlinear propagation, Diagnostics

Abstract:
The theory of wave reflection from spherical obstacles was applied for determination of the cause of the shadow created by plane wave pulses incident on rigid, steel, gaseous spheres and on spheres made of kidney stones. The spheres were immersed in water which was assumed to be a tissuelike medium. Acoustic pressure distributions behind the spheres with the radii of 1 mm, 2.5 mm and 3.5 mm were determined at the frequency of 5 MHz. The use of the exact wave theory enabled us to take into account the diffraction effects. The computed pressure distributions were verified experimentally at the frequency of 5 MHz for a steel sphere with a 2.5-mm radius. The experimental and theoretical pulses were composed of about three ultrasonic frequency periods. Acoustic pressure distributions in the shadow zone of all spheres were shown in the amplitude axonometric projection, in the grey scale and also as acoustic isobar patterns. Our analysis confirmed existing simpler descriptions of the shadow from the point of view of reflection and refraction effects; however, our approach is more general, also including diffraction effects and assuming the pulse mode. The analysis has shown that gaseous spherical inclusions caused shadows with very high dynamics of acoustic pressures that were about 15 dB higher in relation to all the other spheres. The shadow length, determined as the length at which one observes a 6-dB drop of the acoustic pressure, followed the relation r−6dB = 3.7a2λ with the accuracy of about 20% independent of the sphere type. λ denotes the wavelength and a the sphere radius. Thus, a theoretical possibility of differentiating between gaseous and other inclusions and of estimation of the inclusion size in the millimeter range from the shadow was shown. The influence of the frequency-dependent attenuation on the shadow will be considered in the next study.

Keywords:
Shadow, Pulses, Spheres, Ultrasonography

Abstract:
The aim of the paper was a preliminary comparison of heating efficiency by the two physically different modalities, namely ultrasound sonication and alternating magnetic field, of magnetic nanoparticles added to an agar-gel. Special agar-based tissue mimicking material (TMM) were manufactured from agar with the addition of produced by us iron oxide magnetic nanoparticles of order c/a 11 nanometers. To perform comparison of heating by the measured temperature rise curves caused by the two physical fields differently acting on the material sample, in the case of ultrasonic radiation we did not locate the sensor of thermometer in the ultrasonic beam focus, as it was usually studied, but we put it in the place where distribution of ultrasound intensity was more homogeneous. It was motivated by the fact that the “homogeneous heating” by the magnetic iron oxide nanoparticles which are spatially homogeneously distributed should be compared with the ultrasonic heating effects caused by the spatially homogeneous ultrasonic sources. The obtained results confirm that for both fields, ultrasound and magnetic, the temperature increase was caused by the presence of nanoparticles. In the case of heating by magnetic field pure agar-gel was not heated at all, and during sonication the pure agar-gel exhibited very small thermal effect, due only to the structure of the agar-gel crosslinking. We concluded that the ultrasonic absorption was in our experiment greater than magnetic, but the temperature rise after 180 s of magnetic field action was greater than of sonication.

Keywords:
Heating systems, Ultrasonic imaging, Temperature measurement, Acoustics, Magnetic fields, Nanoparticles, Ultrasonic variables measurement

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:
W pracy przedstawiono wstępne wyniki pomiaru pola temperatury wewnątrz tkanki in vitro w czasie procesu nagrzewania wiązką ultradźwiękową o słabej mocy oraz pomiaru właściwości akustycznych wzorców tkanek miękkich. Wzorce te zbudowano w celu dalszych badań nad powiązaniem wzrostu temperatury z właściwościami akustycznymi, gdyż próbki tkankowe in vitro okazały się niepowtarzalne i nietrwałe. Na wykonanych 3 wzorcach tkankowych dokonano pomiaru sygnału przejścia i wyznaczono prędkość propagacji impulsu, współczynnik tłumienia oraz zbadano statystykę rozproszenia. Przedyskutowano wpływ liczby elementów rozpraszających na te wielkości.

Keywords:
wzorce tkanek, sygnał ultradźwiękowy, prędkość dźwięku, tłumienie, statystyka rozproszenia

Abstract:
The paper presents a new yield criterion for the transversal isotropy of metal sheets under plane-stress conditions which is an extension of the isotropic yield function proposed by Burzynski (Burzynski W. l928). Studium nad hipotezami Burzynski's doctoral dissertation „Study on material effort hypotheses”, Engng. Trans., 2009, t. 57, nr 3-4, s. l85-2l5). Two additional coefficients have been introduced in order to allow a better representation of plastic behavior of metal sheets. The proposed yield condition includes the influence of first invariant of the stress tensor and also the strength differential effect. The system of equations describing the sheet metal forming process is solved by algorithm using the return mapping procedure. PIane stress constraint is incorporated into the Newton-Raphson iteration loop. The proposed algorithm is verified by performing a numerical test using shell elements in commercial FEM software ABAQUS/EXPLICIT with a developed VUMAT subroutine. It is shown that the proposed approach provides the satisfactory prediction of material behavior, at least in the cases when anisotropy effects are not advanced. To perform FE simulations of cup deep drawing processes, three independent yield stresses are required. Those yield stresses can be obtained from: directional uniaxial tensile test, directional uniaxial compression test and equibiaxial compression tests. In the paper the formability of two metal sheets are analysed. First the influence of strength differential effect on the cup height profile is shown. Then the comparison between the Huber-Mises-Hencky yield condition and the proposed yield condition is presented.

Keywords:
bone scanner, trabecular bone, osteoporosis

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. Examples of skin scans obtained with the new thick-film transducers are presented.

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

Abstract:
We used 7 types of samples, ”pure agar-gel” sample (AG), agar-gel doped with graphite micro-particles (GMP), agar-gel doped with magnetic micro-particles (MMP) and agar-gel doped with magnetic nanoparticles (MNP) with every doping in two different proportion of ingredients, namely of weigh percentage of 0.8 and 1.6 of the added particles. In the series of experiments we registered RF echoes of backscattered signals emitted by single-element transducer with focus posed on the metal reflector and in the focus posed inside the samples. From this data the speed of sound, the frequency dependent attenuation and backscatternig coefficient were obtained for every sample. Additionally, densities of sample materials were determined, and the elasticity coefficient and acoustical impedance of every material were calculated under the assumption of linear propagation. From the differences between attenuation and scattering the estimation of absorption were performed. The measurements demonstrated that adding the nanoparticles increased the density of the material compare to adding microparticles made from the same magnetic material. The elasticity coefficient and impedance are proportional to the fraction of particles and the elasticity of phantom components. The most interesting conclusion concerns in comparison of difference in ultrasonic absorption. The absorption of agar-gel with NMP exhibited the largest value in between all studied cases. This allows us to assume that the local heating of the medium by the ultrasonic beam should be more efficient in this case, and dopes of iron oxide nanoparticles can be considered as ”sono-sensitizers” in performing ultrasonic hyperthermia. It is worth noting, that this result was independently confirmed by the measuring of temperature rise during the heating of phantoms by the focused ultrasound beams of different powers. This result is presented in another paper at this conference.

Abstract:
The soft tissue structure possess the multi-scale anatomical inhomogeneities. There are many types of tissues, where one can recognize at least two main scales: millimeter scale and micrometer scale which are the basic scattering structures for an ultrasound wave of the diagnostic frequency range penetrating the tissue. The millimeter scale is due to the existence of quasi-periodic blocks of cells forming semi-regular lobules e.g. in the anatomical units of the liver tissue, and the micrometer scale is formed with many small scatterers like cell walls or large cell nuclei. The breaking of anatomical structure is often caused by the beginning of the cancer process. It is very important and unresolved problem to find any tools in qualitative ultrasound to recognize this two type of scattering. To this end some phantom experiment were performed. 3D thread structure in the form of nylon threads with a thickness of 0.1 mm (or of 0.35 mm) placed at regular periodic structure with distances of 1 mm (or of 1.5 mm) was immersed in the water. This threads structure was used as a model to analyse the properties of ultrasound signal echoes registered with the use of different transducers, both focusing and plane ones. The range of carried frequencies for used transducers were of 1MHz to 15 MHz. Additionally, the threads structure with threads of of 0.35 mm thickness and located in distances of 1.5 mm, immersed in an oil and starch gel instead of the water were · was used to analyse the influence of the background medium properties on the ultrasound backscattering signals. Having measured pulse properties of a transducer and applied the wavelet analysis to the registered signals the identification of the threads positions in space, namely MSS (Mean Scatterer Spacing) was calculated and some aspects of the differences between scattering and reflection phenomena were discussed as a function of ratio between pulse length and geometrical parameters, i.e. threads thickness and distances between them.

Keywords:
attenuation estimation, parametric imaging