Institute of Fundamental Technological Research

Phased-Array Ultrasonic Technique is traditionally used for the non-destructive inspection of welds and supported by industrial-grade inspection equipment. FullMatrix Capture (FMC) with Total Focusing Method (TFM) provide new capabilities and multimodal imaging, but available commercial scanners have limitations in acquisition speed (30–300MB/s) and reconstruction speed. Our goal was to develop a solution for FMC acquisition that can be applied to high-speed robotized weld scanning (speed of 100 mm/s with a resolution of 1 mm). For FMC acquisition, we have applied a portable programmable ultrasound research system us4R-lite™ (us4us Ltd., Poland) in a 64:256 channel configuration and standard angled 32-element Phased-Array probes. The system can acquire and store raw RF or demodulated I/Q data at a speed of 2–6 GB/s, enabling real-time FMC at high speed. Data can be stored on a PC during scanning and processed by a high-performance GPU. We have successfully tested our experimental setup while scanning flat-section welds with a motorized scanner at a speed approaching 100 mm/s. The acquisition and processing software developed uses Nvidia CUDA on GPU and can manage real-time storage and scanning. Next, we are planning to integrate the solution into an industrialgrade high-speed FMC acquisition system with embedded GPU processing.

Ultrasonic Testing (UT) (4285), robotic inspection (23), PAUT (42), FMC (16), TFM (28), GPU processing

Ultrasound shear wave elastography (SWE) has emerged as a promising technique that enables the quantitative estimation of soft tissue stiffness. However, its practical implementation is complicated and presents a number of engineering challenges, including high-energy burst transmission, high-frame rate data acquisition and high computational requirements to process huge datasets. Therefore, to date, SWE has only been available for high-end commercial systems or bulk and expensive research platforms. In this work, we present a low-cost, portable and fully configurable 256-channel research system that is able to implement various SWE techniques. We evaluated its transmit capabilities using various push beam patterns and developed algorithms for the reconstruction of tissue stiffness maps. Three different push beam generation methods were evaluated in both homogeneous and heterogeneous experiments using an industry-standard elastography phantom. The results showed that it is possible to implement the SWE modality using a portable and cost-optimized system without significant image quality losses.

ultrasound imaging, shear wave elastography, high-frame rate imaging, medical system design

W ramach realizowanego projektu wdrożeniowego (akronim: BalTECH, finansowanie NCBR POIR) opracowano modelowe stanowiska skanerow UTPA do badań nieniszczących spawow dla asortymentu produktow wytwarzanych w Baltic Operator sp. z o.o. Skanery zapewniają prowadzenie i sprzężenie dwoch głowic Phased-Array (badanie dwustronne). Do realizacji badań UTPA wykorzystano komercyjny aparat Olympus-OmniScan ™ X3, natomiast dlametody UTPA-FMC (Full-Matrix Capture) badawczą platformę ultradźwiękową us4R-lite™ firmy us4us sp. z o.o. Wykonano zestaw ok. 170 probek testowych spawow z rożnymi niezgodnościami dla płyt w zakresie grubości 12–65 mm, ktore zostały przebadanie metodami VT, MT/PT, UT, RT, UTPA. Opracowana procedura badania i wzorce testowe pozwoliły na pełną walidację klasycznej metody UTPA do badania sekcji wież wiatrowych. Eksperymentalne zastosowanie i porownanie metody UTPA-FMC pokazało jej duży potencjał oraz nowe możliwości wizualizacji i oceny wad, w stosunku do klasycznej metody UTPA. Zweryfikowano także możliwość zbierania surowych danych FMC z prędkością do 100 mm/s. Kluczowe znaczenie ma wdrożenie nowoczesnych i ekonomicznych rozwiązań badań nieniszczących, ktore zapewnią ocenę jakości 100% długości spawu. Istotny wkład w rozwoj laboratoriow badawczych, w kontekście wiarygodności uzyskiwanych wynikow badania.

ultradźwiękowe badania nieniszczące, spawy, Phased-Array, UTPA, FMC

We propose a novel approach to breast mass classification based on deep learning models that utilize raw radio-frequency (RF) ultrasound (US) signals. US images, typically displayed by US scanners and used to develop computer-aided diagnosis systems, are reconstructed using raw RF data. However, information related to physical properties of tissues present in RF signals is partially lost due to the irreversible compression necessary to make raw data readable to the human eye. To utilize the information present in raw US data, we develop deep learning models that can automatically process small 2D patches of RF signals and their amplitude samples. We compare our approach with classification method based on the Nakagami parameter, a widely used quantitative US technique utilizing RF data amplitude samples. Our better performing deep learning model, trained using RF signals and their envelope samples, achieved good classification performance, with the area under the receiver attaining operating characteristic curve (AUC) and balanced accuracy of 0.772 and 0.710, respectively. The proposed method significantly outperformed the Nakagami parameter-based classifier, which achieved AUC and accuracy of 0.64 and 0.611, respectively. The developed deep learning models were used to generate parametric maps illustrating the level of mass malignancy. Our study presents the feasibility of using RF data for the development of deep learning breast mass classification models.

breast lesion classification, convolutional neural networks, deep learning, radio-frequency signals, ultrasound imaging

Building upon the recent successes in the application of information-theoretic concepts (e.g. Shannon entropy) in quantitative ultrasound, the authors propose a novel tissue characterization method based on the Lempel–Ziv complexity. In this procedure, standard ultrasound B-Mode images are mapped onto words over finite alphabets before the corresponding Lempel–Ziv complexity of ultrasound images is calculated. Such complexity metric may be used to differentiate between types of tissues. Here, the method is utilized as a binary classifier for the malignancy of breast lesions. The method is tested on OASBUD – an open-access breast lesions image database. Images of 48 malignant and 48 benign lesions were used – two images for each lesion. The new procedure slightly outperforms the state-of-art classifier based on pixel entropy as measured in the size of area under the receiver operating curve (ROC AUC), which suggests that it may serve as a basis for computer-assisted breast cancer ultrasound diagnosis and possibly in other standard applications of the quantitative ultrasound.

quantitative ultrasound, tissue characterization, speckles, breast cancer, Lempel–Ziv complexity, applied information theory, space-filling curves

Complex flow patterns are prevalent in the vasculature, but they are difficult to image non-invasively in real-time. This paper presents the first real-time scanning platform for a high frame rate ultrasound technique called color encoded speckle imaging (CESI) and its use in visualizing arterial flow dynamics in-vivo. CESI works by simultaneously rendering flow speckles and color-coded flow velocity estimates on a time-resolved basis. Its live implementation was achieved by integrating a 192-channel programmable ultrasound front-end module, a 4.8 GB/s capacity data streaming link, and a series of computing kernels implemented on the graphical processing unit (GPU) for beamforming and Doppler processing. A slow-motion replay mode was also included to offer coherent visualization of CESI frames acquired at high frame rate (3,000 fps in our experiments). The live CESI scanning platform was found to be effective in facilitating real-time image guidance (at least 20 fps for live video display with 55 fps GPU processing throughout). In vivo pilot trials also showed that live CESI, when running in replay mode, can temporally resolve triphasic flow at the brachial bifurcation and can reveal flow dynamics in the brachial vein during a fist-clenching maneuver. Overall, live CESI has potential for use in routine investigations in-vivo that seek to identify complex flow dynamics in real-time and relate these dynamics to vascular physiology.

color-encoded speckle imaging (CESI), complex flow visualization, graphical processing units (GPUs), high-frame-rate ultrasound (HiFRUS), in vivo studies, live scanning platform

The computing performance optimization of the Short-Lag Spatial Coherence (SLSC) method applied to ultrasound data processing is presented. The method is based on the theory that signals from adjacent receivers are correlated, drawing on a simplified conclusion of the van Cittert-Zernike theorem. It has been proven that it can be successfully used in ultrasound data reconstruction with despeckling. Former works have shown that the SLSC method in its original form has two main drawbacks: time-consuming processing and low contrast in the area near the transceivers. In this study, we introduce a method that allows to overcome both of these drawbacks. The presented approach removes the dependency on distance (the "lag" parameter value) between signals used to calculate correlations. The approach has been tested by comparing results obtained with the original SLSC algorithm on data acquired from tissue phantoms. The modified method proposed here leads to constant complexity, thus execution time is independent of the lag parameter value, instead of the linear complexity. The presented approach increases computation speed over 10 times in comparison to the base SLSC algorithm for a typical lag parameter value. The approach also improves the output image quality in shallow areas and does not decrease quality in deeper areas.

short lag spatial coherence, synthetic aperture, algorithm optimization, parallel processing

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.

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

Ultradźwiękowe systemy Phased-Array (PA) umożliwiają detekcję i ocenę wad za pomocą wieloelementowych głowic ze skanowaniem elektronicznym. Zaawansowane metody kierowania wiązki oraz wizualizacji znacznie ułatwiają badania obiektów o skomplikowanej geometrii. Należy jednak pamiętać, ze klasyczna metoda PA bazuje na tych samych zasadach fizycznych, co skanowanie standardowymi głowicami jednoelementowymi i posiada te same ograniczenia. W naszym laboratorium pracujemy nad implementacją nowej klasy metod obrazowania UT, które wykorzystują technikę Full-Matrix Capture (FMC) oraz Total Focusing Method (TFM). Metody te dają zupełnie nowe możliwości rekonstrukcji obrazów wad i pozwalają na uzyskanie jednorodnej rozdzielczości poprzecznej w całej głębokości badania. W tym celu zbudowaliśmy demonstrator przenośnego systemu PA wyposażony w funkcje FMC i TFM. Akwizycja pełnej macierzy ech oraz przetwarzanie softwarowe na wbudowanym procesorze GPU (Nvidia Tegra) zapewniają duże możliwości przetwarzania i analizy sygnałów. Demonstrator jest wyposażony w 32-kanały akwizycji w konfiguracji 32:128 i współpracuje ze standardowymi głowicami PA firmy Olympus.

UT, Phased-Array, akwizycja pełnej macierzy, GPU

A method of suppression of grating lobes is presented, analyzed, and verified. The method is based on creating a Virtual Receiving Subaperture (VRS) by adding virtual transducer elements not existing in the physical layout of the receiver. The VRS channels are filled with data based on signals from real channels. The analytical model of the synthetic aperture imaging system's impulse response is presented to describe the properties of the VRS. The model shows a reduction of the receiving grating lobes' amplitude (with a comparison to the main lobe’s amplitude) by a magnitude equal to the number of receiving transducer elements. It is shown that effective properties of the entire system with a VRS are similar to a system with a pitch in the receiving aperture that is twice as small. The numerical calculations of the impulse response show a doubling of the signal to noise ratio, which results in a reduction of the receiving grating lobes. For experimental validation, the generalized Plane Wave Imaging with and without the VRS is compared with a basic synthetic transmit aperture (STA) imaging. The experiment confirmed that the use of a VRS allows for visualizat ion of the objects in a medium in which they are not imaged without a VRS or are visualized with a lower contrast. The reduction of grating lobes attained using the proposed method is at the level of 15dB in the visualization of the superficial cyst.

grating lobes, image quality, synthetic aperture, virtual subaperture

A new ultrasound digital transcranial Doppler system (digiTDS) is introduced. The digiTDS enables diagnosis of intracranial vessels which are rather difficult to penetrate for standard systems. The device can display a color map of flow velocities (in time-depth domain) and a spectrogram of a Doppler signal obtained at particular depth. The system offers a multigate processing which allows to display a number of spectrograms simultaneously and to reconstruct a flow velocity profile.
The digital signal processing in digiTDS is partitioned between hardware and software parts. The hardware part (based on FPGA) executes a signal demodulation and reduces data stream. The software part (PC) performs the Doppler processing and display tasks. The hardware-software partitioning allowed to build a flexible Doppler platform at a relatively low cost.
The digiTDS design fulfills all necessary medical standards being a new useful tool in the transcranial field as well as in heart velocimetry research.

Doppler system, digital signal processing, hardware-software partitioning, field programmable gate arrays

W artykule przedstawiona została możliwość lokalizacji delaminacji w płycie włóknisto-cementowej za pomocą specjalnie do tego celu skonstruowanego urządzenia wykorzystującego metodę ultradźwiękową i fale podłużne. Przeprowadzono badania na trzech rodzajach płyt. Stwierdzono, że proponowana metoda diagnostyczna umożliwia wykrywanie lokalnych nieciągłości, np. obszarów o obniżonej zwartości, czy delaminacji w płytach włóknisto-cementowych na obszarze średnicy wiązki metodą estymacji prędkości fali ultradźwiękowej. Zaletami metody są niewielkie wymiary urządzenia i krótki czas badania

płyty włóknisto-cementowe, badania nieniszczące, ultradźwięki

Ultradźwiękowe systemy Phased-Array pozwalają na różne tryby skanowania i wizualizacji wad oraz zapewniają wyższą jakość inspekcji niż tradycyjne systemy jednokanałowe. Kolejnym krokiem w rozwoju tych systemów będzie metoda akwizycji pełnej macierzy oraz zaawansowane algorytmy rekonstrukcji obrazów. W artykule przedstawiono zasady działania tych technik oraz wymagania jakie stawiają one przed systemami akwizycji i przetwarzania sygnałów. Zaprezentowano także badawczy system Uniwersalnej Platformy Ultradźwiękowej, który został opracowany specjalnie do testowania i praktycznego wdrażania tych metod. Platforma posłużyła do badań i porównania dwóch metod rekonstrukcji przy wykorzystaniu akwizycji pełnej macierzy – metody STA (Synthetic Transmit Aperture) i metody PWI (Plane Wave Imaging).

UT Phased-Array, akwizycja pełnej macierzy, syntetyczna apertura

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

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

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

thick film transducers, atherosclerosis, flow mediated vasodilation

Nieinwazyjne metody obrazowania serca są nieodłączną częścią współczesnej diagnostyki kardiologicznej. Jakość obrazowania niezależnie od użytej techniki stanowi ważny element interpretacji wyniku. Znajomość najczęstszych artefaktów echokardiografii, tomografii rentgenowskiej (CT, X-ray computed tomography) i badania serca metodą rezonansu magnetycznego (CMRI, cardiac magnetic resonance imaging) oraz sposobu ich uniknięcia jest istotna w codziennej pracy.

obrazowanie medyczne, USG, CT, CMRI

This paper discusses the mechanical properties, microstructure and crystallographic texture of light alloys made on the base of aluminium, magnesium and lithium. An acoustic emission (AE) technique was applied to detect the moment of twinning or slip activation during compression and channel – die tests to extend the comprehension on the nature of the plastic deformation processes occurring in the investigated alloy s

hcp metals, aluminium and magnesium alloys, plastic deformation, mechanical twinning, crystallographic texture, acoustic emission

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.

Synthetic aperture imaging, Ultrasound imaging, Directivity function, Beamforming

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

artificial heart, microemboli, ultrasound Doppler

The paper deals with the problems related to the diagnostics of selected parts of modern Diesel engines. The evolution of mechanical properties of four alloys of Mg-Li-Al system and four composites made on the base of the alloys mentioned above, caused by variation of its composition was presented. The Acoustic Emission (AE) method applied to monitoring of degradation of mechanical properties of the alloys and composites was described. Moreover, the results of the investigation of failures occurring in the injectors of Common Rail Diesel engines per formed with the application of AE method were also reported.

Diesel engines diagnostics, light alloys and composites, Common Rail fuel system, Acoustic Emission method

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

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

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.

cancellous bone, broadband ultrasound attenuation, FPGA

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

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

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

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

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

anticellulite treatment, high-frequency ultrasound

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.

ultrasound imaging, synthetic aperture, beamforming

Prowadzone w IPPT PAN prace mające na celu opracowanie uniwersalnych wielokanałowych systemów ultradźwiękowych do zastosowań medycznych i przemysłowych zaowocowały zaproponowaniem nowych architektur komunikacji i przetwarzania cyfrowego sygnałów w oparciu o procesory wielordzeniowe oraz procesory graficzne (GPU). Opracowana architektura systemów jest skalowalna ze względu na liczbę kanałów i może być zastosowana do systemów jedno- i wielokanałowych. W artykule przedstawiono funkcje i metody realizacji przetwarzania w defektoskopach z analogowym i cyfrowym torem przetwarzania sygnałów. Wskazano na ograniczenia obecnych systemów oraz przedstawiono nową architekturę, która pozwala na pełną programowalność toru przetwarzania. Pokazano przykładowe metody i algorytmy przetwarzania, których implementacja może przyczynić się do znacznego zwiększenia funkcjonalności urządzeń defektoskopowych zbudowanych w oparciu o nową architekturę.

defektoskopia ultradźwiękowa, przetwarzanie sygnałów, procesory GPU

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

ultrasound imaging, synthetic aperture

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.

synthetic aperture method, ultrasound imaging, beamforming

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

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

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.

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

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

high-frequency ultrasonography - cellulite classic ultrasonography ultrasonography

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.

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

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.

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

Ultradźwiękowe metody badań nieniszczących przechodzą obecnie metamorfozę od systemów z głowicami jednoelementowymi do systemów wielokanałowych z głowicami fazowymi (PA Phased Array). Prowadzony obecnie w Zakładzie Ultradźwięków IPPT PAN projekt ma na celu opracowanie uniwersalnej wielokanałowej platformy ultradźwiękowej oraz metod rekonstrukcji obrazów mogących znaleźć zastosowanie zarówno w medycynie, jak i w badaniach nieniszczących. Przeprowadzono wstępne badania mające na celu porównanie różnych metod rekonstrukcji obrazów wad w trybie B-mode. W tym celu dokonano akwizycji ech ultradźwiękowych od wad w szynie kolejowej przy pomocy ultrasonografu badawczego wyposażonego w 128-elementową głowicą fazową o częstotliwości 4 MHz. Uzyskane sygnały ech wysokiej częstotliwości poddano następnie obróbce cyfrowej w celu uzyskania obrazu B-mode. Zastosowano i porównano różne metody rekonstrukcji obrazu: klasyczny beamforming oraz metodę syntetycznej apertury. Wstępne wyniki wskazują na wysoką jakość rekonstrukcji metodą syntetycznej apertury, która zapewnia równomierną rozdzielczość poprzeczną w całej głębokości obrazowania. Zastosowanie alternatywnych schematów nadawczo-odbiorczych w metodzie syntetycznej apertury umożliwia dodatkowo optymalizację metody pod względem prędkości badania lub jakości obrazowania. Wyniki te potwierdzają przydatność i konkurencyjność metody syntetycznej apertury do stosowanej obecnie metody beamformingu.

ultradźwiękowe badania nieniszczące, głowice Phased-Array, metody syntetycznej apertury

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.

beamforming, frame rate, synthetic aperture, ultrasound imaging

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

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

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.

ultrasonic therapy, annular array transducer, ultrasonic field

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.

ultrasound imaging, synthetic aperture, beamforming

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

synthetic aperture focusing technique, ultrasonic imaging

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

skin characterization, ultrasound, K distribution

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

bone structure, bone properties, calcaneus

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

ultrasound imaging, synthetic aperture, frame rate, beamforming

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

attenuation coefficient, backscattering coefficient, dermis

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

RF signal simulation, scattering on blood cells, pulsed Doppler

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

ultrasound imaging, synthetic aperture, beamforming

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

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

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

ultrasound imaging, synthetic aperture, contrast resolution

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

Golay complementary sequences, double pulse transmission, dead zone

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

ultrasound, transducer, bandwidth, Golay code

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

Coded excitation, Ultrasound field distribution, Matching filtering

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

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

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

coded excitation, sound fields

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

Golay complementary sequences, double transmission, dead zone

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

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

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

Background, Motivation and Objective
Flexible ultrasound (US) arrays are a promising technology that may further democratize US technology — e.g. in wearable US. Flexible transducers also pose challenges in image reconstruction, as they require adaptable beamforming delays due to a changing geometry of the probe. Various approaches have been proposed for flexible array shape estimation and beamforming, e.g. external sensors, deep learning and optimization. In this work, we propose a deep reinforcement learning (DRL) approach, where a software agent is responsible for tracking the array shape to properly reconstruct US B-mode image.

Statement of Contribution/Methods
Here we considered a reinforcement learning environment as a setup consisting of a US system with the flexible array and point targets phantom. The environment was simulated using j-Wave software. The environment’s state consisted of the current shape of the array, modeled as a sinusoid s = a sin(bx + c), and the current model of the array assumed by the beamformer: s’ = a’ sin(b’x + c’) (single-element STA scheme). A single episode consisted of
7 steps; the parameters a, b, c could vary from step to step (within bounds of physical constraints). The agent observed the current B-mode, could modify the current values of a’, b’ and c’ (action) and received a reward equal to the linear combination of the coherence factor and structural similarity index measure (SSIM) between the current and reference image. We trained our agent using TD3 approach and tested it for various settings of a, b and c.

Results/Discussion
Our agent achieved an average SSIM of 0.73 per episode step. Figure 1 shows the sequence of states and images within an example episode; the agent was able to correctly react to the change of the array shape. The DRL approach has the following advantages compared to other methods: the agent can be trained to operate in an environment with a changing state; and the agent can be trained to maximize expected return (dependent on beamforming quality metric), which does not have to be differentiable.

Fig. 1. (Top) B-mode images, estimated array shape (red) and actual shape (black) within an example episode. (Bottom) Coherence factor and SSIM achieved by the agent during the episode

Accurate estimation of the speed-of-sound (SoS) is important for ultrasound (US) image reconstruction techniques and tissue characterization. Various approaches have been proposed to calculate SoS, ranging from tomography-inspired algorithms like CUTE to convolutional networks, and more recently, physics-informed optimization frameworks based on differentiable beamforming. In this work, we utilize implicit neural representations (INRs) for SoS estimation in US. INRs are a type of neural network architecture that encodes continuous functions, such as images or physical quantities, through the weights of a network. Implicit networks may overcome the current limitations of SoS estimation techniques, which mainly arise from the use of non-adaptable and oversimplified physical models of tissue. Moreover, convolutional networks for SoS estimation, usually trained using simulated data, often fail when applied to real tissues due to out-of-distribution and data-shift issues. In contrast, implicit networks do not require extensive training datasets since each implicit network is optimized for an individual data case. This adaptability makes them suitable for processing US data collected from varied tissues and across different imaging protocols. We evaluated the proposed SoS estimation method based on INRs using data collected from a tissue-mimicking phantom containing four cylindrical inclusions, with SoS values ranging from 1480 m/s to 1600 m/s. The inclusions were immersed in a material with an SoS value of 1540 m/s. In experiments, the proposed method achieved strong performance, clearly demonstrating the usefulness of implicit networks for quantitative US applications.

beamforming, deep learning, implicit neural representations, speed-of-sound, quantitative ultrasound

Ultrasound (US) imaging is widely used for the tissue characterization. However, US images commonly suffer from speckle noise, which degrades perceived image quality. Various deep learning approaches have been proposed for US image denoising, but most of them lack the interpretability of how the network is processing the US image (black box problem). In this work, we utilize a deep reinforcement learning (RL) approach, the pixelRL, to US image denoising. The technique utilizes a set of easily interpretable and commonly used filtering operations applied in a pixel-wise manner. In RL, software agents act in an unknown environment and receive appropriate numerical rewards. In our case, each pixel of the input US image has an agent and state of the environment is the current US image. Agents iteratively denoise the US image by executing the following pixel-wise pre-defined actions: Gaussian, bilateral, median and box filtering, pixel value increment/decrement and no action. The proposed approach can be used to generate action maps depicting operations applied to process different parts of the US image. Agents were pre-trained on natural gray-scale images and evaluated on the breast mass US images. To enable the evaluation, we artificially corrupted the US images with noise. Compared with the reference (noise free US images), filtration of the images with the proposed method increased the average peak signal-to-noise ratio (PSNR) score from 14 dB to 26 dB and increased the structure similarity index score from 0.22 to 0.54. Our work confirms that it is feasible to use pixel-wise RL techniques for the US image denoising.

deep reinforcement learning, ultrasound imaging, image denoising, filtration, breast cancer

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.

ultrasound imaging, 3D ultrasound, volumetric imaging, gpu

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

Ultrasound is becoming the modality of choice for everyday medical diagnosis, due to its mobility and decreasing price. As the availability of ultrasound diagnostic devices for untrained users grows, appropriate guidance becomes desirable. This kind of support could be provided by a software agent, who easily adapts to new conditions, and whose role is to instruct the user on how to obtain optimal settings of the imaging system during an examination. In this work, we verified the feasibility of implementing and training such an agent for ultrasound, taking the deep reinforcement learning approach. The tasks it was given were to find the optimal position of the transducer’s focal point (FP task) and to find an appropriate scanning plane (PP task). The ultrasound environment consisted of a linear-array transducer acquiring information from a tissue phantom with cysts forming an object-of-interest (OOI). The environment was simulated in the Field-II software. The agent could perform the following actions: move the position of the probe to the left/right, move focal depth upwards/downwards, rotate the probe clockwise/counter-clockwise, or do not move. Additional noise was applied to the current probe setting. The only observations the agent received were B-mode frames. The agent acted according to stochastic policy modeled by a deep convolutional neural network, and was trained using the vanilla policy gradient update algorithm. After the training, the agent’s ability to accurately locate the position of the focal depth and scanning plane improved. Our preliminary results confirmed that deep reinforcement learning can be applied to the ultrasound environment.

ultrasound guidance, reinforcement learning, deep learning

Portable and hand-held ultrasound imagers have the potential to revolutionize Point-of-Care medical diagnostics. There is great need for low-cost, portable scanners with extended battery life. In this paper, we focus on hardware-software partitioning in heterogeneous systems where both field-programmable gate array (FPGA) and graphics processing unit (GPU) resources are available. We present the architecture of a prototype test scanner for the evaluation of various hardware-software partitioning strategies. The system is equipped with the Intel Arria 10 FPGA and the Nvidia Tegra X2 mobile GPU. FPGA-based beamformers: Delay-and-Sum and Filtered Multiply-and-Sum, were implemented. These 32-channel beamformer blocks are integrated into a complete dataflow along with the data acquisition, RF filter, quadrature demodulator, and envelope detector. The designed dataflow allows one to allocate processing functions to either hardware (FPGA) or software (GPU) to explore various imaging scenarios and optimize power consumption. A dedicated measurement setup facilitates measuring power consumption of both FPGA and GPU. The developed setup will provide a reliable experimental system power characterization.

ultrasound imaging, ultrasound scanner, point-ofcare ultrasound, beamforming, low-power, FPGA, GPU processing

The paper describes two different techniques of ultrasound measurements performed in fibre cement boards, the material widely applied in building technology. An in-house device dedicated for fibre-cement board testing is also presented. To overcome the difficulty of determining the arrival time of the waveform of a longitudinal wave travelling across a thin and inhomogeneous body, a cross-correlation method of signal processing was proposed and applied

ultrasound, fibre-cement board, waveform cross correlation coefficient

The widely adopted ultrasound Phased-Array (PA) systems for nondestructive testing (NDT) use standard beamforming for line-by-line image creation. The introduction of the new full-matrix capture (FMC) technique enables the implementation of advanced processing algorithms (e.g. the total focusing method, multi-pass adaptive techniques). However, the limited availability of portable PA systems with FMC capabilities prevents widespread introduction. Our goal was to demonstrate the feasibility of a portable PA solution with FMC and advanced processing with the help of a mobile GPU. Using an OEM ultrasound front-end module (us4us Ltd., Poland), we integrated a complete PA system with an embedded Nvidia Tegra X2 module. An external probe adapter enables a direct connection to commercial Olympus-NDT PA probes with up to 128-elements (32-element active RX aperture). The system is fully programmable, both in the front-end (TX/RX schemes, acquisition parameters), as well as in the digital signal processing chain. Raw RF data is acquired and transferred to mobile GPU memory for processing. The algorithm can be conveniently implemented using a standard Nvidia CUDA toolkit. We implemented real-time B-mode imaging with the total focusing method for demonstration purposes. The presented all-in-one system is a fully flexible tool for the research and evaluation of novel Phased-Array FMC methods and complex signal processing algorithms. An extended programmability and real-time access to raw channel data allows to create custom solutions specifically dedicated to any one NDT application. Mobile GPU parallel processing provides a strong enough performance for real-time imaging. Its small size and low-power consumption make the system an ideal candidate for a portable industrial flaw detector with advanced processing.

Ultrasound medical diagnostics is a real-time modality based on a doctor's interpretation of images. So far, automated Computer-Aided Diagnostic tools were not widely applied to ultrasound imaging. The emerging methods in Artificial Intelligence, namely deep learning, gave rise to new applications in medical imaging modalities. The work's objective was to show the feasibility of implementing deep learning algorithms directly on a research scanner with GPU software beamforming. We have implemented and evaluated two deep neural network architectures as part of the signal processing pipeline on the ultrasound research platform USPlatform (us4us Ltd., Poland). The USPlatform is equipped with a GPU cluster, enabling full software-based channel data processing as well as the integration of open source Deep Learning frameworks. The first neural model (S-4-2) is a classical convolutional network for one-class classification of baby body parts. We propose a simple 6-layer network for this task. The model was trained and evaluated on a dataset consisting of 786 ultrasound images of a fetal training phantom. The second model (Gu-net) is a fully convolutional neural network for brachial plexus localisation. The model uses 'U-net'-like architecture to compute the overall probability of target detection and the probability mask of possible target locations. The model was trained and evaluated on 5640 ultrasound B-mode frames. Both training and inference were performed on a multi-GPU (Nvidia Titan X) cluster integrated with the platform. As performance metrics we used: accuracy as a percentage of correct answers in classification, dice coefficient for object detection, and mean and std. dev. of a model's response time. The 'S-4-2' model achieved 96% classification accuracy and a response time of 3 ms (334 predictions/s). This simple model makes accurate predictions in a short time. The 'Gu-net' model achieved a 0.64 dice coefficient for object detection and a 76% target's presence classification accuracy with a response time of 15 ms (65 predictions/s). The brachial plexus detection task is more challenging and requires more effort to find the right solution. The results show that deep learning methods can be successfully applied to ultrasound image analysis and integrated on a single advanced research platform

Ultrasonic imaging, Neural networks, Convolution, Machine learning, Image segmentation, Kernel

The medical management of patients with continuous-flow left ventricular assist devices (LVADs) requires frequent measurement and analysis of various physiological parameters. Among the most important is blood pressure (BP), which cannot be reliably measured by the standard oscillometric method because of an impaired pulsation due to continuous flow. The objective of this work is to show the feasibility of ultrasound-based BP measurement in a portable, easy to use device for patients with LVAD in home-based rehabilitation environments, enabling long-term remote monitoring. We have implemented a BP measurement system which uses continuous wave (CW) Doppler ultrasound for blood flow detection. The system is based on a standard cuff design with custom analog CW circuitry connected to a high-performance, low-power 32-bit microcontroller (ARM Cortex-M7). The uC is responsible for system control, as well as Doppler signal acquisition and processing. A dedicated ultrasound probe equipped with an elastic strap is placed over the radial artery. In the target solution, the cuff pressure and CW signal will be analyzed in real-time to provide systolic and/or mean blood pressure. At present, we have acquired raw signals for off-line analysis. The system was tested in clinical experiments both on healthy patients and patients with three types of commercially available LVADs (HeartWare, HeartMate II and HeartMate III). The observed morphology of Doppler signals in patients with LVADs was much more variable between patients and pumps. In most cases, we were able to estimate the systolic pressure, but the measurement of diastolic pressure was not conclusive. We observed variable blood flow patterns generated by the Lavare cycle (a periodic speed modulation feature of some LVADs), which further complicates the estimation. A prototype of an automatic BP measuring device for patients with rotary LVADs has been demonstrated. In the next step, we are planning an animal validation study with invasive blood pressure monitoring

Biomedical monitoring, Doppler effect, Blood pressure, Blood, Pressure measurement, Ultrasonic variables measurement, Standards

Ultrasound Phased-Array (PA) systems for nondestructive testing (NDT) use standard beamforming for line-byline image creation. New methods utilizing full-matrix capture (FMC) enable the application of advance processing algorithms, such as the total focusing method and multi-pass adaptive techniques for enhanced flaw visualization. The effective FMC data acquisition and its real-time processing require a very high data throughput and powerful computational resources. Most commercial PA systems support some form of FMC acquisition, but the limited external data bandwidth prevents this mode of operation from being useful. We have developed a fully programmable ultrasound research system capable of performing FMC data acquisition and image reconstruction with a high framerate. The ultrasound platform is supporting up to 192 parallel TX/RX electronics channels integrated with an embedded control PC and a GPU cluster for parallel processing. The implemented software libraries give the end-user control over TX/RX schemes, the acquisition process and signal processing algorithms. This all-in-one system is a fully flexible tool for the research and evaluation of novel Phased-Array FMC imaging methods and complex signal processing algorithms.

GPU, ultrasound, Phased-Array

The paper presents chosen results obtained during the investigation of welded joints (laser, spot and friction) tested using acoustic microscopy method. Detection of welds properties and the defects strongly depends on ultrasonic transducer’s parameters. For the purpose of this research a prototype hardware setup was built – enabling evaluation of various types of ultrasonic probes. The system can be easily adjusted to the geometry of an object and is well equipped with appropriate software for the analysis and processing of images such as B-scan or C-scan. The setup enables determination of welds geometry, in particular the depth of the weld penetration in some cases.

spot welds, high frequency ultrasonic imaging

This paper is a part of the IUS 2016 Planewave Imaging Challenge submission. Spatial compounding of several low-resolution images taken from different angles is a well-established practice in ultrasound imaging. The usual procedure relies on averaging several images using arithmetic mean. An alternative approach is presented, which relies on multiplication of the low-resolution images.

ultrasound, plane wave imaging

Systemy UT z głowicami wieloelementowymi Phased-Array (PA) zapewniają wyższą jakość inspekcji i prędkość badania oraz różne mody skanowania i wizualizacji wad. Dostępne na rynku przenośne systemy PA zapewniają skanowanie i rekonstrukcję obrazów 2D w czasie rzeczywistym w oparciu o wyliczone i zaprogramowane prawa ogniskowania (ang. focal laws). Ta klasyczna metoda rekonstrukcji linii A-scan, z których następnie tworzony jest obraz 2D, nosi nazwę beamformingu. Metoda beamformingu podlega tym samym zasadom i ograniczeniom co badanie za pomocą równoważnej głowicy jednoelementowej (tj. o tej same aperturze, kącie i ogniskowaniu).
W referacie postaram się przedstawić zasadę działania metod syntetycznej apertury w sposób intuicyjny oraz zaprezentuję przykłady nowych aplikacji tej metody. Zainteresowanych odsyłam także do moich prezentacji zakopiańskich z lat ubiegłych, które dotyczyły podstaw fizycznych i metod rekonstrukcji w technice Phased-Array.

badania nieniszczące, technika ultradźwiękowa, systemy Phased-Array

Ultrasound transmit push sequences put a high stress on a pulser IC due to power dissipation that could result in overheating. The aim of this work was to determine the safe range of parameters of push sequences for a high-voltage, high-speed, 4-channel pulser STHV748 (STMicroelectronics). The impact of using ceramic capacitors and electrolytic capacitors on the HV supply was also examined. The reaction of the pulser was measured with three output loading conditions. A safe range of values of pulser voltage for a given transmit frequency and sequence length were determined by monitoring chip temperature. Additionally, maximum pulse repetition frequency was evaluated in function of the maximum supply voltage. The STHV748 pulser is capable of generating push sequences. The duty-cycle is a key parameter that determines the safe operating conditions of the pulser. Limiting the amplitude of the HV supply enables us to increase push burst duration or decrease the frequency of the transmit signal.

acoustic radiation force, shear wave imaging, push sequences, HV pulser

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

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

In spite of the progress in material engineering and ventricular assist devices construction, thromboembolism remains the most crucial problem in mechanical heart supporting systems. Therefore, the ability to monitor the patient’s blood for clot formation should be considered an important factor in development of heart supporting systems. The well-known methods for automatic embolus detection are based on the monitoring of the ultrasound Doppler signal. A working system utilizing ultrasound Doppler is being developed for the purpose of flow estimation and emboli detection in the clinical artificial heart ReligaHeart EXT. The system will be based on the existing dual channel multi-gate Doppler device with RF digital processing. A specially developed clamp-on cannula probe, equipped with 2 − 4MHz piezoceramic transducers, enables easy system setup. We present the issues related to the development of automatic emboli detection via Doppler measurements. We consider several algorithms for the flow estimation and emboli detection. We discuss their efficiency and confront them with the requirements of our experimental setup. Theoretical considerations are then met with preliminary experimental findings from a) flow studies with blood mimicking fluid and b) in-vitro flow studies with animal blood. Finally, we discuss some more methodological issues - we consider several possible approaches to the problem of verification of the accuracy of the detection system.

microemboli, embolism, Doppler ultrasound, ventricular assist device

ultradźwiękowe badania nieniszczące, głowice Phased-Array

The Synthetic Aperture (SA) method provides a new solution in ultrasound diagnostics. It has particular importance in applications where frame rate and image resolution are crucial. Our new approach named Cumulative Synthetic Transmit Aperture (CSTA) allows optimizing SA in terms of memory size and computational power. The proposed CSTA algorithm requires 25 times less memory than a reference STA method for 64 elements transducer. This makes feasible implementation of CSTA on a low-power embedded GPU.

ultrasonic imaging, synthetic aperture, GPU

Our goal is to develop a complete ultrasound platform based on real-time SAFT (Synthetic Aperture Focusing Technique) GPU processing. We are planning to integrate all the ultrasound modules and processing resources (GPU) in a single rack enclosure with the PCIe switch fabric backplane. The first developed module (RX64) provides acquisition and streaming of 64 ultrasound channels. We implemented and benchmarked data streaming from the RX64 to the GPU memory and the SAFT image reconstruction on the GPU. A high system performance was achieved using hardware assisted direct memory transfers and pipelined processing workflow. The complete system throughput, including 128 channel data transfer at 16kS per line and low-resolution 256×256 pixel image SAFT reconstruction on a single Nvidia K5000 GPU, reached 450 fps. The obtained results proved the feasibility of the ultrasound real-time imaging system with GPU SAFT processing.

ultrasonic imaging, synthetic aperture, GPGPU, FPGA

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.

synthetic aperture, ultrasound imaging, beamforming

The synthetic aperture focusing techniques (SAFT) are well known and widely deployed in radar techniques. Increasing processing power of modern computers allows effective implementation of various SAFT schemes in medical ultrasound systems with multi-element probes. The advance of the SAFT over the classical beamforming (BFR) is dynamic focusing in receive and transmit as well, which brings high resolution on every imaging point. We intend to develop the ultrasound imaging platform with some of the SAFT schemes implemented. The choice of the scheme must be preceded by examination of the imaging quality parameters. The results of the comparison of different SAFT schemes with conventional beamforming are presented in the paper. The results indicate that SAFT schemes can work better than BFR scheme. For example, for some point located near the center of the image the full width at half maximum (FWHM) was equal approximately 0.5, 0.4 and 0.3 mm, while the contrast-to-noise ratio (CNR) was equal 18, 19, and 19 dB for BFR, STA and PWI respectively.

Ultrasonic imaging, SAFT, Plane Wave Imaging

The objective of our project is to develop a complete ultrasound platform with real-time GPU processing. The platform is designed to be modular and scalable both in number of ultrasound channels (64-256), as well as in communication bandwidth and processing power. By standardizing on the PCIe switch fabric, we are planning to integrate all the ultrasound modules and processing resources (GPU) in a single rack enclosure. Using PCIe direct peer-to-peer communication for transferring the data from the ultrasound acquisition modules to the GPUs, we maximize the system bandwidth and minimize CPU usage. The first developed module of our platform is RX64 - a 64-channel ultrasound acquisition PCIe card. The RX64 contains a high-end FPGA Altera Stratix IV 70 GX interfaced to: two 32-channels mixed-signal front-end ultrasound modules and two 64-bit 8GB DDR3 SO-DIMM memories for data buffering. We also develop GPU kernels for SAFT based ultrasound imaging, as well as GPU Framework for building complete signal processing pipeline.

ultrasonic imaging, synthetic aperture, GPU, FPGA

There is a continuous trend towards small and portable ultrasound systems with multichannel processing. The objective of the work was to develop a modular acquisition and processing platform based on the following architecture principles: limited hardware processing, external high-speed data communication and software based on SAFT processing using embedded graphics processing unit (GPU). The acquisition module connected via PCIe or USB 3.0 interface can stream either raw RF data or demodulated ones. A low-power embedded PC with embedded GPU will implement ultrasound signal processing, as well as control and visualization functions. The performed feasibility study showed that AMD APU G-Series embedded x86 CPU+GPU is capable of real-time SAFT image reconstruction at limited resolution.

ultrasonic imaging, synthetic aperture, medical electronics, GPU, FPGA

GPU computing is a new paradigm in high performance signal and image processing. Massive parallel processing offered by the GPUs provides high acceleration of computations when they are properly implemented. Ultrasound image reconstruction is one of these highly parallel classes of algorithms. Massive amount of multichannel input data and deterministic order of execution makes US applications good candidates for high performance GPU implementation. Our goal is to design a versatile ultrasound platform with GPU real-time processing. The project is based on a new system architecture allowing for bandwidth and scalability of processing power. We implemented and optimized SAFT image reconstruction algorithms on CUDA. The study shows that a single GTX-580 GPU card is capable of reconstructing the 128-channel I/Q data into 256×256 High Resolution Images (HRI) at a frame-rate of 44.64 fps which is an equivalent of 5700 Low Resolution Images (LRI) per second.

ultrasonic imaging, synthetic aperture, GPU, CUDA

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.

bone scanner, trabecular bone, osteoporosis

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.

Golay codes, coded sequences, synthetic aperture, ultrasound imaging

Increasing efforts are currently dedicated to incorporate the Synthetic Transmit Aperture (STA) method in ultrasound imaging systems. The STA technique can provide a pixel-like focusing (dynamic focusing at both transmit and receive) without impairment of the frame rate. This goal can only be achieved by a careful design of the transmission and reception schemes. In this paper, the preliminary results of resolution, Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) measurements for a specific SA scheme with different transmit apertures are presented. The measurements were made using a novel ultrasound advanced open platform (ULA-OP) developed at the University of Florence. The ULA-OP is fully programmable and enables access to the RF echo-data from each transducer element.

synthetic aperture, ultrasound open platform

Acoustical waves scattered in trabecular bone contain information about its microstructural properties. These properties may change on course of a disease. Standard ultrasonic examinations of bone (densitometry) are performed in transmission and does not provide complete information about bone strength. We have developed the bone ultrasonic scanner that enables measurements of the physical properties of trabecular bone microstructure. Thus the evaluation of bone properties using ultrasonic scanner may be essential for bone diseases diagnosis and treatment monitoring. This study presents application of the scanner operating at 1,5 MHz frequency for examination of trabecular bone (calcaneus). Backscattered data were collected and processed in order to obtain power backscattering coefficient (PBSC). Calculated values were compared to these published by several authors in order to verify ultrasonic scanner application as a tool for trabecular bone examination. This study is an approach towards developing a method for the investigation of scattering in trabecular bone that can potentially provide clinically useful information about bone strength and condition.

trabecular bone, bone scanner, osteoporosis

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.

synthetic aperture, ultrasound imaging

Metody ultradźwiękowego obrazowania struktur wewnętrznych człowieka są nieustannie ulepszane. Opracowywane są nowe algorytmy umożliwiające poprawę niektórych parametrów wynikowych. Przykładem jest metoda syntetycznej apertury (SA), która pozwala wyświetlać obrazy o wysokiej rozdzielczości z większą częstotliwością niż standardowa metoda formowania wiązki.
Ograniczeniem metody SA jest większa złożoność obliczeniowa, która przy znacznej ilości danych może uniemożliwić osiągnięcie pożądanej szybkości rekonstrukcji. Problem ten można ominąć rezygnując z części zarejestrowanych sygnałów. Wiąże się to oczywiście z pogorszeniem jakości obrazowania, jednak przy odpowiedniej technice przerzedzania danych degradacja obrazu jest niewielka. Proponowany sposób przerzedzania ma zastosowanie w metodzie syntetycznej apertury nadawczej (STA) i opiera się na założeniu, że sygnał uzyskany za pomocą dowolnej pary przetworników jest taki sam niezależnie od tego, który z przetworników nadawał, a który odbierał. W tej sytuacji można pominąć blisko połowę zapisanych danych i wciąż
możliwe będzie zrekonstruowanie obrazu w poprzedniej jakości. Na podstawie prezentowanych wyników symulacji oraz pomiarów na fantomach nitkowym i tkankowym wykazano, że stosując opisaną technikę przerzedzania można zmniejszyć o połowę ilość danych przy zachowaniu rozdzielczości i nieznacznym spadku parametru SNR oraz kontrastu rekonstruowanych obrazów.

metody syntetycznej apertury, przerzedzanie danych

The Synthetic Aperture (SA) methods are widespread and successfully used in radar technology, as well as in the sonar systems. The advantages of relatively good resolution in the whole area of scanning without decrease of framerate, make this technique an object of interest in medical imaging methods such as ultrasonography (US).This paper describes the possible usage of the SA method in ultrasound imaging. The measurements of different SA schemes were conducted using the set-up consisting of the research ultrasonograph module, the PC and the special wire phantom. The results for different schemes of image reconstruction are presented. Particularly the Synthetic Transmit Aperture (STA) technique was concerned. Results of the STA method are discussed in this paper.

ultrasonic imaging, synthetic aperture focusing technique

W artykule opisano wybór i implementację filtrów ech stałych w programowalnych układach logicznych (FPGA) dla ultradźwiękowego wielobramkowego systemu przezczaszkowego przepływomierza krwi opracowywanego w Zakładzie Ultradźwięków IPPT PAN. Implementacja filtrów w FPGA miała na celu redukcję obciążenia softwarowego przetwarzania sygnałów dopplerowskich. W pracy przedstawiono badania modelowe i porównanie filtrów ech stałych o skończonej odpowiedzi impulsowej (SOI) oraz nieskończonej odpowiedzi impulsowej (NOI). Przeanalizowany został zakres stabilnej pracy filtru NOI. Wyselekcjonowany filtr górnoprzepustowy typu SOI został następnie zaimplementowany i zoptymalizowany do architektury układów FPGA oraz zastosowania w przepływomierzu. Zastosowano ekonomiczny układ FPGA Altera Cyclone III EP3C25F324C8. Opracowany filtr ech stałych realizuje 100 identycznych górnoprzepustowych filtrów typu SOI, co zapewnia filtrowanie sygnału dopplerowskiego w 100 bramkach jednocześnie. Filtry operują na 16 bitowych próbkach sygnału, a ich charakterystyka jest programowalna przez 65 16-bitowych współczynników. Zweryfikowano poprawność przetwarzania na komputerze PC w środowisku Altera Quartus II 9.1 oraz ModelSim 6.5b poprzez symulacje i porównanie odpowiedzi impulsowej oraz skokowej filtrów. W wyniku opisanych prac powstała struktura logiczna filtru ech stałych przeznaczona do implementacji w układzie FPGA Cyclone III, zajmująca 5% zasobów logicznych układu oraz 34% zasobów pamięciowych.

ultradźwiękowy Doppler przezczaszkowy, filtry ech stałych, cyfrowe przetwarzanie, FPGA

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.

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

Doppler instruments are widely used for evaluation of the hemodynamic of vascular circulation. The objective of the work was to develop a modular acquisition and processing system to enable the construction of various ultrasound instruments. The developed system consists of two electronic boards with dimensions of 130x82mm in sandwich configuration. Digital signal processing was based on an efficient DSP (Blackfin BF537, Analog Devices, USA) with 128MB RAM and an FPGA (Cyclone III EP3C25, Altera, USA). The system can work as a standalone device with the limited user interface or as a PC peripheral under the control of the application software. The dual channel transcranial PW Doppler flowmeter with multigate processing has been the first application of the developed platform. The acquisition module provides the A/D sampling at 64 MSPS rate with 14-bits resolution and supports ultrasonic transducers within the range of 1–16 MHz. The PC software performs signal processing and visualization of color Doppler, spectrum, flow profile and audio. The developed system is a modern technical solution which enables to build portable Doppler instruments of different classes. The developed prototype of transcranial Doppler will be introduced into production soon.

ultrasound Doppler systems, transcranial aplications, digital RF processing, DSP, FPGA

Determination of attenuating properties of the tissue from the echoes of waves emitted by the focused transducer requires to compensate the echo signal for the effects of focusing. We propose the diffraction/focusing effects correcting (FC) technique that compensates focusing-induced mean frequency
shift (MFS) of the propagating pulse. The method corrects mean frequency estimates derived from echo pulses propagating in attenuating tissue with locally varying attenuation coefficient. The FC algorithm applies the diffraction correcting coefficients obtained experimentally from the probing pulses focused in water for assessing the expected values of MFS of pulses focused in attenuating tissue. The calculations involves the pulse ‘history’ that due to overall attenuation along the traveled path downshifts the pulse spectrum resulting in variation of the focusinginduced MFS obtained in water.

attenuation estimation, difraction correction, parametric imaging

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 complementary Golay sequences (CGS). Two different bit lengths were investigated, specifically one and two cycles. Three transducers having fractional bandwidth of 25%, 58% and 80% and operating at frequencies 6 MHz, 4.4 MHz and 6 MHz, respectively were examined (one of the 6 MHz sources was 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 indicate 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 transducers two cycles excitation would not decrease the time resolution, obtained with ’conventional’ spike excitation. These results also indicate that CGS excitation could be successfully implemented with the existing, relatively narrow band imaging transducers without the need to use usually more expensive wide-band, composite ones.

ultrasound imaging, coded transmission, transducer badnwidth, Golay codes

anning electron microscopy, in-situ mechanical tests, hot-pressing

In this work, we present a low-cost, portable, and fully configurable ultrasound system implementing 2-D real-time Shear Wave Elastography (SWE) imaging mode. To achieve that we have enhanced the transmit capabilities of the 256 TX/64 RX us4R-lite research system, developed by our team, to support push pulses generation. This system was combined with a signal processing pipeline reconstructing stiffness maps from raw RF data. Real-time imaging performance was provided by an efficient reconstruction algorithm execution that incorporated graphics processing unit (GPU). The overall system performance was assessed experimentally using an industry-standard elasticity Q/A phantom. Relevant reconstruction parameters were evaluated in terms of reconstruction time. The system achieved stiffness estimation with a bias <5% and SNR of 30 dB and was able to detect lesions of size >4 mm and various stiffness with CNR in the range of 13–17 dB. The system throughput of up to 5 fps has been achieved on a PC notebook equipped with NVIDIA RTX 3060 GPU.

The ultimate goal of this work is a real-time processing framework for ultrasound image reconstruction augmented with machine learning. To attain this, we have implemented WaveFlow – a set of ultrasound data acquisition and processing tools for TensorFlow. WaveFlow includes: ultrasound Environments (connection points between the input raw ultrasound data source and TensorFlow) and signal processing Operators (ops) library. Raw data can be processed in real-time using algorithms available both in TensorFlow and WaveFlow. Currently, WaveFlow provides ops for B-mode image econstruction (beamforming), signal processing and quantitative ultrasound. The ops were implemented both for the CPU and GPU, as well as for built-in automated tests and benchmarks. To demonstrate WaveFlow’s performance, ultrasound data were acquired from wire and cyst phantoms and elaborated using selected sequences of the ops. We implemented and valuated: Delay-and-Sum beamformer, synthetic transmit aperture imaging (STAI), planewave imaging (PWI), envelope detection algorithm and dynamic range clipping. The benchmarks were executed on the NVidiaR Titan X GPU integrated in the USPlatform research scanner (us4us Ltd., Poland). We achieved B-mode image reconstruction frame rates of 55 fps, 17 fps for the STAI and the PWI algorithms, respectively. The results showed the feasibility of realtime ultrasound image reconstruction using WaveFlow operatorsin the TensorFlow framework. WaveFlow source code can be found at github.com/waveflow-team/waveflow.

Preceding atherosclerosis is an endothelial dysfunction. Therefore there is a growing interest in the application of non - invasive clinical tools to assess endothelial function. Commercially available ultrasound machines can measure flow - mediated vasodilatation of the brachial artery using maximum 10-12 MH z linear probes. The higher the probe frequency, the better the axial resolution. Recently, a new technology of piezoelectric transducers based on PZT thick film technology has been developed in Meggitt (Denmark) as a response to a call for devices working at higher frequencies. The thick films exhibited at least 30% bandwidth broadening comparing to the standard PZ 27 transducers, resulting in an increase in match filtering encoding output by a factor of 1.4 - 1.5 and finally resulting in a signal to noise gain of the same order. The introduction of a high frequency 25 - 30 MHz ultrasound scanner to measure radial artery diameter after reactive hyperemia open s a new window for more precise imaging of endothelial function.

thick film transducers, atherosclerosis, flow mediated vaso dilation

A new 128 channel parallel acquisition module for the Ultrasonix SonixTouch ultrasound scanner was developed. Although the module provides similar functionality to the original SonixDAQ system, it presents new possibilities of real-time data streaming and processing on GPU, thanks to a fast PCIe communication interface. Direct access and processing of pre-beamformed channel data with fully programmable transmit schemes enables the research implementation of new advanced imaging modalities (eg. plane wave imaging, vector Doppler, shear wave elastography). The presented RX-DAQ system is enriched with a GPU software framework, for Python and Matlab, enabling the integration of user processing functions.

ultrasonic imaging, pre-beamformed data, real-time processing, GPU, FPGA

A new ultrasound digital transcranial Doppler system (digiTDS) is introduced. The digiTDS enables diagnosis of intracranial vessels which are difficult to penetrate for standard systems. The device can display a color map of flow velocities in time-depth domain and a spectrogram of a Doppler signal received from a particular depth. The system offers a multigate processing that allows to display simultaneously a number of spectrograms and to reconstruct a flow velocity profile. The digital signal processing in digiTDS is partitioned between hardware and software parts. The hardware part (based on FPGA) executes a signal demodulation and reduces data stream. The software part (PC) performs the Doppler processing and display tasks. The hardware-software partitioning allowed to build a flexible Doppler platform at a relatively low cost. The digiTDS design fulfills all necessary medical standards being a new useful tool in transcranial field as well as in heart velocimetry research.

ultrasound transcranial Doppler, RF signal processing, DSP, FPGA