Staff

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:
Portable, hand-held ultrasound devices capable of 3D imaging in real time are the next generation of the medical imaging apparatus adapted not only for professional medical stuff but for a wide group of less advanced users. Limited power supply capacity and the relatively small number of channels used for the ultrasound data acquisition are the most important limitations that should be taken into account when designing such devices and when developing the corresponding image reconstruction algorithms. The aim of this study was to develop a new 3D ultrasound imaging method which would take into account the above-mentioned features of the new generation of ultrasonic devices – low-cost portable general access scanners. It was based on the synthetic transmit aperture (STA) method combined with the Fourier spectrum domain (SD) acoustic data processing. The STA using a limited number of elements in transmit and receive modes for ultrasound data acquisition allowed both aforementioned constraints to be obeyed simultaneously. Moreover, the computational speed of the fast Fourier transform (FFT) algorithm utilized for the ultrasound image synthesis in the spectrum domain makes the proposed method to be more competitive compared to the conventional time domain (TD) STA method based on the delay-and-sum (DAS) technique, especially in the case of 3D imaging in real time mode. Performance of the proposed method was verified using numerical 3D acoustic data simulated in the Field II program for MATLAB and using experimental data from the custom design 3D scattering phantom collected by means of the Verasonics Vantage 256™ research ultrasound system equipped with the dedicated 1024-element 2D matrix transducer. The method proposed in this paper was about 80 times faster than its counterpart based on the time domain synthetic transmit aperture (TD-STA) approach in the numerical example of a single 3D ultrasound image synthesized from 4 partial images each containing 64 × 64 × 512 pixels. It was also shown that the acceleration of the image reconstruction was achieved at the cost of a slight deterioration in the image quality assessed by the contrast and contrast-to-noise ratio (CNR).

Keywords:
ultrasound imaging, matrix transducer, delay-and-sum, Fourier transform

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:
The objective of this paper is an experimental study of the most crucial parameters of the received acoustic signals (e.g. signal-to-noise ratio (SNR), side-lobes level (SLL), axial resolution) obtained as a result of si-multaneous emission of mutually orthogonal Golay complementary sequences (MOGCS) to demonstrate their feasibility of being used in ultrasound diagnostics. Application of the MOGCS in ultrasound measurements allows the image reconstruction time to be shortened without decreasing the resulting quality of econstructed images in comparison with regular complementary Golay coded sequences (CGCS). In this paper two sets of 16-bits long MOGCS were implemented in the Verasonics VantageTM (Verasonics Inc., Kirkland, WA, USA) scanner. Ultrasound data were generated using a perfect reflector, a custom-made nylon wire phantom and tissue mimicking phantom. Parameters of the detected MOGCS echoes like SNR, SLL and axial resolution were determined and compared to that of the standard CGCS and the short two-sine cycles pulse. It was evidenced that applying MOGCS did not compromise the parameters of the separated and compressed echoes in compa-rison to the other types of transmitted signal – the CGCS and the short pulse. Concretely, both the MOGCS and CGCS yield similar SNR increase in comparison to the short pulse. Almost similar values of the axial reso-lution estimated at the full width at the half maximum level for all types of the transmitted signals were also obtained. At the same time, using the MOGCS the data acquisition speed can be increased twice in comparison with the CGCS signal.

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

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:
Accurate evaluation of ultrasonic wave attenuation is important in many medical applications of ultrasound. The aim of this work is to present a thorough analysis of the effectiveness of using complementary Golay coded sequences (CGCS) during the evaluation of ultrasound attenuation in tissue-like materials, especially at greater depths or at high attenuation. In order to compare the results of the attenuation measurement with the use of CGCS transmission and a short two sine cycles pulse, ultrasound backscattered from medium with predefined attenuation of 0.3, 0.7 and 2 dB/[MHz×cm] were simulated. Also for the same transmission signals, measurements of ultrasound echoes scattered in the tissue phantom with an attenuation of 0.5 dB/[MHz×cm] were performed. In the case of numerically simulated data, for the CGCS excitation, the maximum depth for which the attenuation was correctly determined increased from 55 mm to 80 mm for the 0.7 dB/[MHz×cm] phantom and from 20 mm to 50 mm for the 2 dB/[MHz×cm] phantom compared to excitation of the transducer with a short two sine cycles pulse. When the measurement data obtained using the tissue phantom was used to estimate the attenuation coefficient, the relative error was determined to be 6% and 16% for the depths of 10 mm and 40 mm for the short two sine cycles pulse excitation, respectively. Corresponding values for CGCS excitation and considered depths were 2% and 4%. The use of CGSC sequence during attenuation measurements increases measurement accuracy and can improve medical diagnostic techniques.

Keywords:
attenuation, coded excitation, Golay sequences, ultrasound imaging

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:
The purpose of this work was to present a new approach that allows the influence of cortical bone on noninvasive measurement of broadband ultrasound attenuation (BUA) to be corrected. The method, mplemented here at 1 MHz makes use of backscattered signal and once refined and clinically confirmed, it would offer an alternative to ionizing radiation based methods, such as DEXA (Dual-nergy X-ray absorptiometry), quantitative computed tomography (QCT), radiographic absorptiometry (RA) or single X-ray absorptiometry (SXA), which are clinically approved for assessment of progress of osteoporosis. In addition, as the method employs reflected waves, it might substantially enhance the applicability of BUA - from being suitable to peripheral bones only it would extend this applicability to include such embedded bones as hip and femoral neck. The proposed approach allows the cortical layer parameters used for correction and the corrected value and parameter of the ancellous bone (BUA) to be determined simultaneously from the single (pulse-echo) bone backscattered wave; to the best of the authors' knowledge such approach was not previously reported. The validity of the method was tested using acoustic data obtained from a custom- esigned bone-mimicking phantom and a calf femur. The relative error of the attenuation coefficient assessment was determined to be 3.9% and 4.7% for the bone phantom and calf bone specimens, respectively. When the cortical shell influence was not taken into account the corresponding errors were considerably higher 8.3% (artificial bone) and 9.2% (calf femur). As indicated above, once clinically proven, the use of this BUA measurement technique in reflection mode would augment diagnostic power of the attending physician by permitting to include bones, which are not accessible for transmission mode evaluation, e.g. hip, spine, humerus and femoral neck.

Keywords:
broadband ultrasound attenuation, correction of influence of cortical bone, trabecular bone

Abstract:
Commercially available cardiac scanners use 64–128 elements phased-array (PA) probes and classical delay-and-sum beamforming to reconstruct a sector B-mode image. For portable and hand-held scanners, which are the fastest growing market, channel count reduction can greatly decrease the total power and cost of devices. The introduction of ultra-fast imaging methods based on plane waves and diverging waves provides new insight into heart's moving structures and enables the implementation of new myocardial assessment and advanced flow estimation methods, thanks to much higher frame rates. The goal of this study was to show the feasibility of reducing the channel count in the diverging wave synthetic aperture image reconstruction method for phased-arrays. The application of ultra-fast 32-channel subaperture imaging combined with spatial compounding allowed the frame rate of approximately 400 fps for 120 mm visualization to be achieved with image quality obtained on par with the classical 64-channel beamformer. Specifically, it was shown that the proposed method resulted in image quality metrics (lateral resolution, contrast and contrast-to-noise ratio), for a visualization depth not exceeding 50 mm, that were comparable with the classical PA beamforming. For larger visualization depths (80–100 mm) a slight degradation of the above parameters was observed. In conclusion, diverging wave phased-array imaging with reduced number of channels is a promising technology for low-cost, energy efficient hand-held cardiac scanners.

Keywords:
phased-array, ultrasound imaging, diverging wave, synthetic transmit aperture

Abstract:
The paper presents a method that allows the thickness of a compact bone layer and longitudinal wave velocity in the bone to be determined simultaneously with the use of reflected waves, with particular emphasis on the case of layers when the propagation time through the layer is shorter than the time duration of the interrogating pulse.

The proposed method estimates simultaneously the thickness of the cortical bone layer and acoustic wave velocity by fitting the temporal spectrum of the simulated reflected wave to the spectrum of the reflected wave measured experimentally. For the purpose of echo-simulations the model of “soft tissue – compact bone layer – cancellous bone” was developed. Next, the cost function was defined as the least square error between the measured and simulated temporal spectra. Minimization of the cost function allowed us to determine the values of the parameters of the cortical bone layer which best fitted the measurements. To solve the optimization problem a simulated annealing algorithm was used.

The method was tested using acoustic data obtained at the frequency of 0.6 MHz and 1 MHz respectively for a custom designed bone mimicking phantom and a calf femur. For the cortical shell of the calf femur whose thickness varies from 2.1 mm to 2.4 mm and velocity of 2910 m/s, the relative errors of the thickness estimation ranged from 0.4% to 5.5%. The corresponding error of the acoustic wave velocity estimation in the layer was 3.1%. In the case of artificial bone the thickness of the cortical layer was equal to 1.05 and 1.2 mm and acoustic wave velocity was 2900 m/s. These parameters were determined with the errors ranging from 1.9% to 10.8% and from 3.9% to 4.5% respectively.

Keywords:
Bone quantitative ultrasound, Human cortical bone, Human cancellous bone, Ultrasound attenuation, Layered media

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 aim of this work is to present preliminary results of the layer thickness assessment method based on optimization approach. The developed method is based on a multilayer model structure. The measured acoustic signal reflected from the layer is compared with a simulated signal on the basis of a multilayer model. The cost function is defined as the difference between the reflected signal measured using pulse echo approach and the simulated signal. The thickness of the solid layer is the parameter which minimizes the cost function yielding desired solution. Minimization of the cost function is performed with the simulated annealing algorithm. The results obtained with the developed method using measurement data of a custom design model are compared with the reference value and the accuracy of the method is checked. The relative error of the thickness estimation is 1.44 %.

Keywords:
Bone quantitative ultrasound, Human cortical bone, Human cancellous bone, Ultrasound attenuation, Layered media

Abstract:
The paper presents an overview of theoretical aspects of ultrasound image reconstruction techniques based on the circular Radon transform inversion. Their potential application in ultrasonography in a similar way as it was successfully done in the x-ray computer tomography is demonstrated. The methods employing Radon transform were previously extensively explored in the synthetic aperture radars, geophysics, and medical imaging using x-ray computer tomography. In this paper the main attention is paid to the ultrasound imaging employing monostatic transmit-receive configuration. Specifically, a single transmit and receive omnidirectional source placed at the same spatial location is used for generation of a wide-band ultrasound pulse and detection of back-scattered waves. The paper presents derivation of the closed-form solution of the CRT inversion algorithms by two different approaches: the range-migration algorithm (RMA) and the deconvolution algorithm (DA). Experimentally determined data of ultrasound phantom obtained using a 32-element 5 MHz linear transducer array with 0.48 mm element pitch and 0.36 mm element width and 5 mm height, excited by a 2 sine cycles burst pulse are used for comparison of images reconstructed by the RMA, DA, and conventional synthetic aperture focusing technique (SAFT). It is demonstrated that both the RMA and SAFT allow better lateral resolution and visualization depth to be achieved as compared to the DA approach. Comparison of the results obtained by the RMA method and the SAFT indicates slight improvement of the lateral resolution for the SAFT of approximately 1.5 and 1.6% at the depth of 12 and 32 mm, respectively. Concurrently, however, the visualization depth increase for the RMA is shown in comparison with the SAFT. Specifically, the scattered echo amplitude increase by the factor of 1.36 and 1.12 at the depth of 22 and 32 mm is demonstrated. It is also shown that the RMA runs about 30% faster than the SAFT and about 12% faster than the DA method.

Keywords:
synthetic aperture focusing method, circular Radon Transform, delay-and-sum beamforming, range migration algorithm

Abstract:
Assessment of cortical bone thickness is important from a medical point of view because bone-layer thickness has a diagnostic value. The thinning of the cortical bone layer reduces the mechanical strength of the bone and exposes it to an increased risk of osteoporotic fractures [1]. The hip bone (proximal femur) is the most critical fracture site. The thickness of the cortical layer in the proximal femur is often too thin to be detected from ultrasonic echoes using traditional peak detection methods (for example the envelope method). In such a case the cepstrum analysis technique may be very useful. In this study the cepstrum method was applied to analyze numerically simulated echoes reflected from the layer and to determine layer thickness. In simulation, the transducer operated at 1 MHz and pulses of a 1.5 microsec. duration were assumed.

Keywords:
cortical bone, thickness, cepstrum analysis

Abstract:
The aim of this work is to present a theoretical analysis of a 2D ultrasound transducer comprised of crossed arrays of metal strips placed on both sides of thin piezoelectric layer (a). Such a structure is capable of electronic beam-steering of generated wavebeam both in elevation and azimuth. In this paper a semi-analytical model of the considered transducer is developed. It is based on generalization of the well-known BIS-expansion method. Specifically, applying the electrostatic approximation, the electric field components on the surface of the layer are expanded into fast converging series of double periodic spatial harmonics with corresponding amplitudes represented by the properly chosen Legendre polynomials. The problem is reduced to numerical solving of certain system of linear equations for unknown expansion coefficients.

Keywords:
beamforming, transducer array, BIS-expansion

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:
Planar systems of electrodes arranged on both sides of dielectric piezoelectric layer are applied in numerous transducers. They are capable of electronic beam-steering of generated wave both in azimuth and elevation. The wave-beam control is achieved by addressable driving of two-dimensional transducer through proper voltage supply of electrodes on opposite surfaces of the layer. In this paper a semi-analytical method of analysis of the considered transducer is proposed, which is a generalization of the well-known BIS-expansion method. It was earlier exploited with great success in the theory of interdigital transducers of surface acoustic waves, theory of elastic wave scattering by cracks and certain advanced electrostatic problems. The corresponding nontrivial electrostatic problem is formulated and solved numerically

Keywords:
beamforming, transducer array, BIS-expansion

Abstract:
Systems of planar electrodes arranged on dielectric or piezoelectric layers are applied in numerous sensors and transducers. In this paper electrostatics of such electrode systems is presented and exploited in the analysis of distributed piezoelectric transducer dedicated to surface elastometry of biological tissues characterized by large Poisson modulus. The fundamental Matlab code for analyzing complex planar multiperiodic electrode systems is also presented.

Keywords:
interdigital transducer, surface elastometry, BIS-expansion

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 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:
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:
Directional excitation and detection of sound in the periodic baffle system are analyzed using the method developed earlier in electrostatics. The phenomenon is exploited in phased array transducers applied in ultrasonography, nondestructive evaluation and testing. The nice feature of the applied method is that the matrices of the resulting system of the equations are relatively easy for computations and that the results satisfy exactly the energy conservation law. Illustrative numerical examples present the far-field wave-beam steering generated in a baffle system that may be considered as a model of a linear ultrasonic transducer array.

Keywords:
Phased array transducers, Bragg scattering, BIS-expansion

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:
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:
Mixed boundary-value problem for periodic baffles in acoustic medium is solved with help of the method developed earlier in electrostatics. The nice feature of the method is that the resulting matrices are relatively easy for computations and that the results satisfy exactly the energy conservation law. Illustrative numerical examples present the wave-beam steering (in the far-field) in a baffle system that may be considered as a model of one-dimensional ultrasonic transducer array.

Keywords:
Sound field calculation, linear phased arrays, BIS expansion, far-field radiation pattern, beam-steering, transducer arrays, composite transducers, scattering, generation, fields

Abstract:
Directional excitation of sound in an aperiodic finite baffle system is analyzed using a method developed earlier in electrostatics.
The solution to the corresponding boundary value problem is obtained in the spatial-frequency domain. The acoustic pressure and normal particle velocity distribution in acoustic media can be easily computed by the inverse Fourier transform (FFT) from their spatial spectra on the baffle plane.
The presented method can be used for linear acoustic phased arrays modeling with finite element size and inter-element interactions taken into account. Some illustrative numerical examples presenting the far-field radiation pattern and wave-beam steering are given.

Keywords:
phased array, beamforming, mixed boundary-value problem, BIS-expansion

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:
A problem of electromagnetic wave scattering by a periodic parallel-plate waveguide array is studied in the paper. The scattered field above the waveguides is sought in the form of a series of spatial harmonics in accordance with the Floquet's theorem, whereas in the waveguide regions it is sought in the form of parallel plate waveguide modes. A Fourier expansion for spatial harmonics amplitudes with coefficients in the form of properly chosen Legendre functions is used to satisfy the boundary and edge conditions by field components in free space above the array. Some numerical results are given.

Abstract:
The spatial field distribution is the most frequent subject of standard electrostatic analysis. In this paper the system of several strips in external spatial-harmonic electric field, which causes the charge distribution on them, is considered. The solution is constructed as a linear combination of certain template functions, evaluated in spectral domain and satisfying the electric boundary conditions on the strips. The problem is analogous to wave scattering; this justifies the application of the wave-scattering terminology (i.e. incident wave for the external field and the corresponding ‘radiation condition’) in the considered nonstandard ‘electrostatic scattering’ problem. The strip total charge and the Bloch harmonics of the ‘scattered’ field are evaluated.

Keywords:
Planar electrodes, Interdigital transducers, EM scattering

Abstract:
In this work, we considered the implementation of a 3D volume reconstruction algorithm for single plane-wave ultrasound insonification. We review the theory behind the Hybrid Spectral-Domain Imaging (HSDI) algorithm, provide details of the algorithm implementation for Nvidia CUDA GPU cards, and discuss the performance evaluation results. The average time required to reconstruct a single data volume using our GPU implementation of the HSDI algorithm was 22 ms. We also present an iso-surface extraction result using a marching cubes algorithm. Our work constitutes a preliminary research for further development and implementation of 3D volume reconstruction using GPU implementation of the spectral domain imaging algorithm.

Keywords:
ultrasound imaging, 3D ultrasound, volumetric imaging, gpu

Abstract:
In the last few decades 3D/4D ultrasonography has been gaining increasing popularity not only as a scientific research topic but also as a new modality of medical imaging in clinical applications. However, design and implementation of 3D/4D device for high quality ultrasound imaging within portable, handheld systems is a technological challenge. Design of transmit/receive (TX/RX) electronics for efficient operation with 2D array transducers, comprised of thousands of elements, enormous amount of input/output data that must be transferred and processed, power consumption limitation are just a few of the difficulties that arise. No less important is development of reliable and numerically efficient algorithms for 3D/4D imaging which should take all these restrictions into account. The main objective of this paper is to present a new hybrid spectral domain imaging (HSDI) method that delivers an original and innovative solution for the technical limitations of modern ultrasonography 3D/4D. The developed image reconstruction method is based on the plane-wave insonification (PWI) with sub-aperture data acquisition combined with frequency domain (FD) data processing. The performance of the method was tested using the Field II simulated acoustic data of 3D cyst phantom. For a 3D low-resolution image (LRI) comprised of 64×64×512 pixels the proposed HSDI method is about 100 times faster, in the case of a single 3D, than its counterpart based on the PWI synthetic aperture time domain (TD) method for a single TX/RX event. On the other hand, the frame rate increase is proportional to the number of sub-apertures used for a single high-resolution image (HRI) synthesis

Abstract:
Estimation of the thickness and sound velocity of cortical bone is important per se as well as for correcting measurements of cancellous bone properties. We propose a method that allows the thickness of a compact bone layer and longitudinal wave velocity in the bone to be determined simultaneously with the use of the reflected waves, with particular emphasis on the 1mm - 3mm thick bone layers corresponding to the thickness of the cortex of the human femur. The method was tested using ultrasonic data obtained from cortical bone phantoms and a fresh calf bone specimen. The results show that the method seems to be well suited to be employed for the determination of the thickness and acoustic wave velocity of the cortical bone layer.

Keywords:
Cortical bone, trabecular bone, thickness and velocities of cortical shell, reflected waves, BUA

Abstract:
A modified multi-element synthetic transmit aperture (MSTA) method for ultrasound imaging with RF echoes correction taking into account the influence of the element directivity is presented. The property is significant as the element width becomes commensurable with the wavelength of the emitted signal. The angular dependence of the radiation efficiency of the transmit/receive aperture is obtained from exact solution of the corresponding mixed boundary-value problem for periodic baffle system, modeling the transducer array. It is evaluated at the nominal frequency of the excitation signal and is implemented in the developed MSTA algorithm as apodization weights calculated for each imaging point and all combinations of the transmit/receive apertures. The performance of developed method is tested using FIELDII simulated synthetic aperture data of the point reflectors to estimate the visualization depth and lateral resolution. Besides, a FIELDII simulated and measurement data of cyst phantom are used for qualitative assessment of the imaging contrast. Comparison of the results obtained by the modified and conventional MSTA algorithms is given which reveals considerable improvement of the image quality in the area neighboring to the transducer’s aperture, and increase of the visualization depth at the cost of slight degradation of lateral resolution near the transducer face.

Keywords:
synthetic aperture, ultrasound imaging, beamforming

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:
Golay codes, coded sequences, synthetic aperture, ultrasound imaging

Abstract:
Synthetic aperture (SA) technique is a novel approach to today's 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 describes the multielement STA method in medical ultrasound imaging with a small number of elements transmitting and all elements receiving apertures. Compared to other methods the multielement STA allows to increase the system frame rate and provides the best compromise between penetration depth and lateral resolution. In the experiments a 32-element linear transducer array with 0.48 mm inter-element 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 tissue mimicking phantom obtained using STA and multielement STA methods are presented to demonstrate the benefits of the second method.

Keywords:
synthetic aperture, ultrasound imaging