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1

Synthetic Aperture Cardiac Imaging with Reduced Number of Acquisition Channels. A Feasibility Study

Tasinkevych Y., Lewandowski M., Klimonda Z., Walczak M.

Archives of Acoustics

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2018

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Vol. 43, No. 3

437--446

EN

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.

2

Electrostatic methods in analysis of acoustic beam-forming structures

Tasinkevych Y.

IPPT Reports on Fundamental Technological Research

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2012

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nr 3

3-159

EN

The work aims to present extensions of the developed methods used in electrostatic analysis of planar periodic and ?nite systems for e?cient solving of variety of the acoustic and electromagnetic wave generation and scattering problems. Specifically, their generalization for application in the acoustic beamforming analysis is reported. Moreover, certain electromagnetic wave scattering problems by periodic waveguiding structures which can be e?ciently approached by these methods are also considered. The monograph consists of seven Chapters. The Chapter 1 presents the introduction where the main objectives of the work are outlined. Mathematical principles of the electrostatic methods which are dealt with in the following are presented in details in the Chapter 2. The cases of in?nite periodic and finite aperiodic systems of in?nitesimally thin electrodes (conducting strips), generally having arbitrary widths and spacings, are considered separately. In the Chapter 3 the electrostatic methods are generalized and extended to the acoustic beam-forming analysis by linear transducer arrays. The mixed boundary-value problem is stated and solved for the cases of infinite periodic and finite aperiodic arrays of rigid baffles. Also, the developed method of the angular directivity function evaluation for a linear transducer array with arbitrary excitation is presented. In the Chapters 4 and 5 several examples illustrating practical applicability of the developed methods are discussed. Specifically, in the Chapters 4 a developed modified multi-element synthetic transmit aperture algorithm for ultrasound imaging, which incorporates the developed method of linear transducer array modeling, is reported. And in the Chapter 5 a two-dimensional electrostrictive transducer array is analyzed. In the Chapter 6 generalization of the electrostatic methods to the electromagnetic wave scattering analysis is presented. Speci?cally, the problems of electromagnetic wave scattering by periodic gratings like a thick-walled parallel-plate waveguide array and a periodic system of conducting electrodes of finite thickness are considered. Finally, the Chapter 7 concludes the monograph.

PL

Podstawowym celem pracy jest przedstawienie opracowanych uogólnionych metod analizy zagadnień elektrostatyki układów planarnych zarówno periodycznych jak i nieperiodycznych, zawierających skończoną ilość elementów, do celów efektywnego rozwiązywania zagadnień brzegowych w teorii generacji i detekcji fal akustycznych oraz analizy zagadnień brzegowych w teorii fal elektromagnetycznych dla przypadku struktur falowodowych. Monografia składa się z siedmiu Rozdziałów. Rozdział 1 stanowi wprowadzenie w którym omówiony został cel i zakres pracy. Matematyczne podstawy metod elektrostatyki, rozwijane i generalizowane w dalszej części monografii, zostały szczegółowo omówione w Rozdziale 2. Tu osobno rozpatrzono przypadki periodycznego oraz nieperiodycznego układów infinitezymalnie cienkich elektrod (przewodzących pasków), w ogólnym przypadku o różnych szerokościach oraz odstępach. W Rozdziale 3 przedstawiono uogólnienie metod elektrostatyki do analizy mieszanego zagadnienia brzegowego dla układów sztywnych przegród, zarówno periodycznych jak i zawierających skończoną ilość elementów, oraz zaprezentowano opracowany model analityczno-numeryczny do obliczania charakterystyki promieniowania liniowych szyków przetworników akustycznych dla dowolnego pobudzenia. Przykłady praktycznego zastosowania opracowanych metod przedstawione zostały w Rozdziałach 4 oraz 5. Mianowicie, w Rozdziale 4 zaprezentowano oryginalny nowoczesny algorytm wieloelementowej syntetycznej apertury nadawczej (ang. multi-element synthetic transmit aperture) dla obrazowania ultrasonograficznego, w którym została zaimplementowana opracowana metoda modelowania liniowych szyków przetworników ultradźwiękowych. Z kolei w Rozdziale 5 przedstawiona została analiza modelu dwuwymiarowej macierzy przetworników elektrostrykcyjnych. W Rozdziale 6 przedstawiono uogólnienie metod elektrostatyki do analizy zjawisk rozpraszania fal elektromagnetycznych dla periodycznych struktur falowodowych takich jak periodyczny układ falowodów płaskich o grubych ściankach oraz periodyczny układ przewodzących elektrod o skończonej grubości. Na koniec, Rozdział 7 przedstawia podsumowanie monografii.

3

Optimization of the Multi-element Synthetic Transmit Aperture Method for Medical Ultrasound Imaging Applications

Tasinkevych Y., Trots I., Nowicki A., Lewandowski M.

Archives of Acoustics

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2012

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Vol. 37, No. 1

47-55

EN

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 Ž 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.

4

Golay Coded Sequences in Synthetic Aperture Imaging Systems

Trots I., Tasinkevych Y., Nowicki A., Lewandowski M.

Archives of Acoustics

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2011

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Vol. 36, No. 4

913-926

EN

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.

5

Wave Generation by a Finite Baffle Array in Application to Beam-Forming Analysis

Tasinkevych Y.

Archives of Acoustics

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2010

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Vol. 35, No. 4

677-686

EN

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 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 wavebeam steering are given.

6

Multi-Element Synthetic Transmit Aperture in Medical Ultrasound Imaging

Trots I., Nowicki A., Lewandowski M., Tasinkevych Y.

Archives of Acoustics

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2010

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Vol. 35, No. 4

687-699

EN

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.

7

Full-wave Analysis of Periodic Baffle System in Beamforming Applications

Tasinkevych Y., Danicki E.

Archives of Acoustics

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2010

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Vol. 35, No. 4

661-675

EN

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.

8

Electromagnetic scattering by a periodic array of thick-walled parallel plate waveguides

Tasinkevych Y.

Journal of Technical Physics

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2009

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Vol. 50, no 1

41-53

EN

Electromagnetic wave scattering by a periodic array of semi-infinite thick-walled parallel plate waveguides is studied in this paper. The cases of TE and TM polarization of an incident plane harmonic wave are considered separately. 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. To satisfy the boundary and edge conditions by field components in the free space above the array, the Fourier expansion for spatial harmonics amplitudes with corresponding coefficients, being properly chosen Legendre functions, is exploited. The unknown coefficients are the solutions of certain doubly infinite systems of linear equations. The approximate solution is found numerically.

9

Plane wave scattering by an infinite array of semi-infinite thick plates

Tasinkevych Y.

Journal of Technical Physics

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2007

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Vol. 48, no 3-4

147-162

EN

The problem of plane electromagnetic wave scattering by periodic system of semi-infinite thick plates of rectangular shape is solved in this paper. The case of TM-polarization is considered in this paper. The field distribution in the free space region above the plates is found in the form of series of spatial harmonics in accordance with the Floquet's theorem. In the plate region the field is found in the form of parallel-plate waveguide modes. The continuity condition for tangential components of electric and magnetic field vectors is applied in order to find unknown partial wave amplitudes. To satisfy the boundary conditions and the singular behavior of the electric field vector near the plate edges, the use is made of the known properties of certain Fourier expansion with corresponding coefficients being properly chosen Legendre functions. The final rigorous solution is given in the form of infinite series of spatial harmonics with unknown coefficients being the solution of the corresponding doubly infinite system of linear equations which can be solved only numerically.

10

Methods of IDT charge spatial spectrum evaluation

Tasinkevych Y.

Journal of Technical Physics

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2004

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Vol. 45, no 2

155-172

EN

Interdigital transducers (IDTs) have found numerous applications in electronic devices for excitation and detection of surface acoustic waves (SAWs). This paper discusses the methods of solution of the electrostatic problem arising in modelling of the IDT most important characteristic - its frequency response. Numerical results are presented based on the so-called spectral approach. Computation difficulties are discussed and their solutions are proposed.