Improved Beamforming for Lateral Oscillations in Elastography Using Synthetic Aperture Imaging

International audienc

Software for ultrasound image generation and acoustic beamform

Orientador: Eduardo Tavares CostaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O diagnóstico médico por ultra-som vem sendo amplamente difundido, tornando se referência em muitos exames clínicos. Por meio das imagens por ultra-som é possível representar a anatomia de tecidos e órgãos de forma não-invasiva, em "tempo real" e sem a utilização de radiação ionizante. A construção de equipamentos de geração de imagens por ultra-som exige um conjunto confiável de circuitos e componentes eletrônicos, de forma a excitar os transdutores ultra-sônicos e também receber os sinais refletidos de forma rápida e robusta. Entretanto, há também a necessidade da utilização de softwares capazes de processar os sinais ultra-sônicos e gerar as imagens de maneira eficiente. Esse trabalho teve como objetivo primário o desenvolvimento de um software código aberto para formação de imagens por ultra-som, empregando técnicas de formação de imagem por ultra-som em "tempo real". O feixe acústico produzido pelos transdutores matriciais do tipo array pode ser defletido e/ou focalizado pela ativação eletrônica dos elementos do transdutor. Dessa forma, como objetivo secundário, foram desenvolvidos circuitos digitais que geram os estímulos com as seqüências de ativação dos elementos transdutores, para que o feixe acústico seja defletido ou focalizado em uma dada distância ou ângulo a partir da face do transdutor matricial. Os circuitos digitais foram criados utilizando FPGA's. O software de geração de imagens bidimensionais por ultra-som, batizado de ImageB, foi desenvolvido em linguagem C++ com Qt Toolkit 4, com estrutura modular, pode ser estendido por meio de plug-ins além de ser multiplataforma e de licença livre. Além dos algoritmos clássicos para conversão do sinal de RF para imagem em escala de cinza, o software incorpora também as técnicas de abertura e focalização sintética (SAFT e SF). O software e o hardware desenvolvidos nesse trabalho foram testados com um transdutor matricial linear de doze elementos, com freqüência central de ressonância de 1MHz. Foi possível observar que os circuitos foram capazes de defletir e focalizar o feixe acústico e o software ImageB foi capaz de gerar imagens dinâmicas de uma estrutura conhecida (phantom de laboratório), trabalhando de forma paralela e integrada com o hardware desenvolvidoAbstract: The ultrasound medical diagnosis has been widely used, becoming a reference in many clinical procedures. Ultrasound imaging makes it possible to represent the anatomy of organs and tissues in a non-invasive, real time way and without using ionizing radiation. The construction of ultrasound imaging systems requires a set of reliable circuits and electronic components, for exciting the ultrasonic transducers and receiving the reflected signals in a fast and robust way. However, one has to use software capable to efficiently process the received ultrasound signals and generate images. This work, as primary objective, aimed at the development of an open-source software for ultrasound image formation, employing techniques for real time ultrasound image formation. The acoustic beam produced by array transducers can be steered and/or focused by electronic activation of the elements of the transducer. As secondary objectives, digital circuits were developed to generate the sequence of activation of the transducer elements in order to steer and focus the acoustic beam electronically over the region of interest at a given distance or angle from the face of the transducer array. These digital circuits were created using FPGA's. The software to generate two-dimensional ultrasound images, ImageB, was developed in C++ with Qt Toolkit 4, has been designed in a modular form, can be extended via plug-ins and is multiplatform and freeware. Besides the traditional algorithms for conversion of the RF signal to grayscale image, the software also incorporates the techniques of aperture and synthetic focus (SAFT and SF). The hardware and software developed in this work were tested using a 1 MHz 12-element array transducer. It was possible to notice that the circuits were capable to steer and focus the acoustic beam and the software ImageB was capable to generate dynamic ultrasound images of a known structure (laboratory phantom), working with the developed hardware in an integrated and parallel wayMestradoEngenharia BiomedicaMestre em Engenharia Elétric

Estimation du mouvement de la paroi carotidienne en imagerie ultrasonore par une approche de marquage ultrasonore

This work focuses on the processing of biomedical images. The aim of our study is to estimate the mechanical properties of the carotid artery in vivo using ultrasound imaging, in order to detect cardiovascular diseases at an early stage. Over the last decade, researchers have shown interest in studying artery wall motion, especially the motion of the carotid intima-media complex in order to demonstrate its significance as a marker of Atherosclerosis. However, despite recent progress, motion estimation of the carotid wall is still difficult, particularly in the longitudinal direction (direction parallel to the probe). The development of an innovative method for studying the movement of the carotid artery wall is the main motivation of this thesis. The three main contributions proposed in this work are i) the development, the validation, and the clinical evaluation of a novel method for 2D motion estimation of the carotid wall, ii) the development, the simulation and the experimental validation of the 3D extension of the estimation method proposed, and iii) the experimental evaluation of the 2D proposed method in ultra-fast imaging, for the estimation of the local pulse wave velocity. We propose a motion estimation method combining tagging of the ultrasound images, and a motion estimator based on the phase of the ultrasound images. The ultrasonic tagging is produced by means of transverse oscillations. We present two different approaches to introduce these transverses oscillations, a classic approach using a specific apodization function and a new approach based on filtering. The proposed motion estimator uses the 2D analytical phase of RF images using the Hahn approach. This thesis work shows that, compared with conventional methods, the proposed approach provides more accurate motion estimation in the longitudinal direction, and more generally in directions perpendicular to the beam axis. Also, the experimental evaluation of our method on ultra-fast images sequences from carotid phantom was used to validate our method regarding the estimation of the pulse wave velocity, the Young’s modulus of the vessels wall, and the propagation of a longitudinal movement.Ce travail de thèse est axé sur le domaine du traitement d’images biomédicales. L’objectif de notre étude est l’estimation des paramètres traduisant les propriétés mécaniques de l’artère carotide in vivo en imagerie échographique, dans une optique de détection précoce des pathologies cardiovasculaires. L’étude des comportements dynamiques de l’artère pour le dépistage précoce de l’athérosclérose constitue à ce jour une piste privilégiée. Cependant, malgré les avancées récentes, l’estimation du mouvement de la paroi carotidienne reste toujours difficile, notamment dans la direction longitudinale (direction parallèle au vaisseau). L’élaboration d’une méthode innovante permettant d’étudier le mouvement de la paroi carotidienne constitue la principale motivation de ce travail de thèse. Les trois contributions principales proposées dans ce travail sont i) le développement, la validation, et l’évaluation clinique d’une méthode originale d’estimation de mouvement 2D adaptée au mouvement de la paroi carotidienne, ii) la validation en simulation, et expérimentale de l’extension à la 3D de la méthode d’estimation proposée, et iii) l’évaluation expérimentale de la méthode proposée, en imagerie ultrasonore ultra-rapide, dans le cadre de l’estimation locale de la vitesse de l’onde de pouls. Nous proposons une méthode d’estimation de mouvement combinant un marquage ultrasonore dans la direction latérale, et un estimateur de mouvement basé sur la phase des images ultrasonores. Le marquage ultrasonore est réalisé par l’intermédiaire d’oscillations transverses. Nous proposons deux approches différentes pour introduire ces oscillations transverses, une approche classique utilisant une fonction de pondération spécifique, et une approche originale par filtrage permettant de contrôler de manière optimale leurs formations. L’estimateur de mouvement proposé utilise les phases analytiques des images radiofréquences, extraites par l’approche de Hahn. Ce travail de thèse montre que la méthode proposée permet une estimation de mouvement plus précise dans la direction longitudinale, et plus généralement dans les directions perpendiculaires au faisceau ultrasonore, que celle obtenue avec d’autres méthodes plus traditionnelles. De plus, l’évaluation expérimentale de la méthode sur des séquences d’images ultrasonores ultra-rapides issues de fantômes de carotide, a permis l’estimation locale de la vitesse de propagation de l’onde de pouls, la mise en évidence de la propagation d’un mouvement longitudinal et enfin l’estimation du module de Young des vaisseaux

Ultrasound Imaging

In this book, we present a dozen state of the art developments for ultrasound imaging, for example, hardware implementation, transducer, beamforming, signal processing, measurement of elasticity and diagnosis. The editors would like to thank all the chapter authors, who focused on the publication of this book

Beamforming Scheme for 2D Displacement Estimation in Ultrasound Imaging

International audienceWe propose a beamforming scheme for ultrasound imaging leading to the generation of two sets of images, one with oscillations only in the axial direction and one with oscillations only in the lateral direction. Applied to tissue elasticity imaging, this leads to the development of a specific displacement estimation technique that is capable of accurate estimation of two components of the displacement. The mean standard deviation for the axial displacement estimates is 0.0219 times the wavelength of the axial oscillations , and for the lateral estimates, it is equal to 0.0164 times the wavelength of the lateral oscillations . The method is presented and its feasibility is clearly established by a simulation work

Beamforming Scheme for 2D Displacement Estimation in Ultrasound Imaging

International audienceWe propose a beamforming scheme for ultrasound imaging leading to the generation of two sets of images, one with oscillations only in the axial direction and one with oscillations only in the lateral direction. Applied to tissue elasticity imaging, this leads to the development of a specific displacement estimation technique that is capable of accurate estimation of two components of the displacement. The mean standard deviation for the axial displacement estimates is 0.0219 times the wavelength of the axial oscillations , and for the lateral estimates, it is equal to 0.0164 times the wavelength of the lateral oscillations . The method is presented and its feasibility is clearly established by a simulation work