Shear wave elastography based on noise correlation and time reversal

Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to image the tissue's shear elasticity. Recent technological developments have allowed SWE to be implemented in commercial ultrasound and magnetic resonance imaging systems, quickly becoming a new imaging modality in medicine and biology. However, coherent shear wave tracking sets a limitation to SWE because it either requires ultrafast frame rates (of up to 20 kHz), or alternatively, a phase-lock synchronization between shear wave-source and imaging device. Moreover, there are many applications where coherent shear wave tracking is not possible because scattered waves from tissue’s inhomogeneities, waves coming from muscular activity, heart beating or external vibrations interfere with the coherent shear wave. To overcome these limitations, several authors developed an alternative approach to extract the shear elasticity of tissues from a complex elastic wavefield. To control the wavefield, this approach relies on the analogy between time reversal and seismic noise cross-correlation. By cross-correlating the elastic field at different positions, which can be interpreted as a time reversal experiment performed in the computer, shear waves are virtually focused on any point of the imaging plane. Then, different independent methods can be used to image the shear elasticity, for example, tracking the coherent shear wave as it focuses, measuring the focus size or simply evaluating the amplitude at the focusing point. The main advantage of this approach is its compatibility with low imaging rates modalities, which has led to innovative developments and new challenges in the field of multi-modality elastography. The goal of this short review is to cover the major developments in wave-physics involving shear elasticity imaging using a complex elastic wavefield and its latest applications including slow imaging rate modalities and passive shear elasticity imaging based on physiological noise correlation

Elastographie et retournement temporel des ondes de cisaillement (application à l'imagerie des solides mous)

L'interaction onde-matière a toujours été un sujet d'étude en Physique, c est le cas de la propagation des ondes élastiques dans le corps humain qu a conduit à plusieurs modalités d'imagerie. En particulier, les techniques d'elastographie reposent sur l'utilisation des ondes de cisaillement pour obtenir une image élastique des tissus mous. Dans ce contexte, cette thèse présente une étude des différentes techniques d'élastographie, en prêtant particulier attention aux aspects plus fondamentaux comme à ces potentielles applications.Tout d'abord, cette thèse montre que l'élastographie impulsionnelle unidimensionnelle (1D) peut être utilisée pour évaluer l'élasticité des couches de tissue d'épaisseur inférieure à la longueur d'onde utilisée. A cet effet, des simulations et des expériences ont été réalisées avec différents fantômes formés par une couche mince immergée dans un milieu d'élasticité différente. La concordance entre expériences et simulations, ainsi que le valeur de l'élasticité obtenue par élastographie 1D et le valeur de l'élasticité intrinsèque de la couche permettent de valider cette technique. Au même temps ces résultats ont été comparés avec ceux obtenus par la technique de Supersonic Shear Imaging (SSI), où l'onde est guidée le long de la plaque. On ajustant la courbe de dispersion expérimentale obtenue par SSI avec un modèle de Lamb, l'élasticité intrinsèque de chaque plaque est estimée. Les résultats obtenus par élastographie 1D et SSI montrent un bon accord entre eux. Le principal avantage de l'élastographie 1D est qu il n'est pas nécessaire d'utiliser un modèle pour estimer l'élasticité de la plaque. Deuxièmement, deux nouvelles modalités d'imagerie quantitative pour l'extraction de élasticité des tissus mou à partir d'un champ élastique complexe sont approfondies: l'Elastographie par Retournement Temporel et le filtre inverse passif. Le but de ces deux techniques est d'estimer localement l'élasticité des tissus, par la mesure de la taille de la tâche focale dans une expérience virtuelle de retournement temporel avec des ondes de cisaillement. A partir de l'étude du processus de retournement temporel dans les solides mous, la faisabilité de ces deux techniques est démontrée in vitro dans des échantillons "bi-couche" et in vivo dans le foie et les muscles, en utilisant le bruit physiologique naturel crée par l'activité cardiaque et musculaire. L'efficacité de l'élastographie par retournement temporel diminue dans le cas d'un champ diffus non isotrope. L'emploie du filtre inverse adaptée à une configuration de source de bruit, permet de rétablir l'isotropie du champ et d'améliorer la résolution pour la détection de petites inclusions. Le filtre inverse passif permet, de surcroît, de contrôler la fréquence qui domine le champ de retournement temporel. Ceci est exploité, dans la dernière partie du manuscrit, pour mener la première expérience de spectroscopie passive en volume. Deux situations sont envisagées: la dispersion due à la propagation d'ondes guidées dans des plaques minces et la dispersion des ondes due à la viscosité.The interaction between wave and matter has long been studied in Physics. In particular, regarding medical applications, wave propagation through the human body resulted in several imaging modalities, each of which uses a specific type of wave linked to a given physical property. The elasticity of soft biological tissues is directly linked to its shear wave speed. Thus, in Elastography, shear waves are tracked for non-invasive assessment of the mechanical properties of soft tissues. In this context, this thesis proposes a study of different elastography techniques from a basic point of view, as well as from its potential applications. Firstly, in this manuscript, the use of 1D transient elastography for the quantitative elasticity assessment of thin layered soft tissues is proposed. Experiments on three phantoms with different elasticities and plate thicknesses were performed. Experimental shear wave speed estimations inside the plate were obtained and validated with finite difference simulation. In addition, the Supersonic Shear Imaging (SSI) technique was performed. For the SSI technique, the propagating wave inside the plate is guided as a Lamb wave. Experimental SSI dispersion curves were fitted using a generalized Lamb model to retrieve the plate bulk shear wave speed. Finally both techniques resulted in similar shear wave speed estimations. The main advantage of 1D transient elastography is that the bulk shear wave speed can be directly retrieved from a time of flight measurement without requiring a dispersion model. Secondly, throughout this thesis, two novel quantitative imaging modalities for extracting the soft tissue's elasticity from a complex reverberated diffuse elastic field are deepen: Time Reversal Elastography (TRE) and the passive inverse filter. The goal of both techniques is to locally estimate the tissue's elasticity, by measuring the focal spot size in a virtual time reversal experiment involving shear waves. By studying the Physics of a time reversal process in soft solids, the feasibility of both techniques as a quantitative imaging techniques is demonstrated in vitro in bi-layer phantoms and in vivo in the liver-belly muscle, by using the physiological noise due to heartbeats and muscular activity. The efficiency of TRE decreases in the presence of a non-isotropic diffuse field. The use of the inverse filter adapted to a passive source configuration, restores the isotropy of the field. As a consequence, the resolution of the elasticity images is improved, leading to a better detection of small inclusions. In addition, the passive inverse filter allows to control the frequency dominating the time reversed field. This is exploited in the last part of the manuscript to conduct the first passive wave spectroscopy experiment in the volume of a soft solid. Two situations are considered: dispersion due to guided wave propagation in thin plates and wave dispersion due to viscosity effects.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Analysis of 1-3 piezocomposite and homogeneous piezoelectric rings for power ultrasonic transducers

Some power ultrasonic transducers, such as Tonpilz transducers, require high-power transmitting capability as well as broadband performance. Optimized vibrational modes can achieve these requirements. This work compares the resonant characteristics and the surface vibration modes between a homogeneous piezoelectric ring and a 1-3 piezocomposite ring, both used in power ultrasonic transducers. This is the first step in the design of power transducers. Analytical models and finite element results are validated by electrical impedance measurements and the surface acoustic spectroscopy method. Excellent agreement between theoretical and experimental results was obtained. Results show that using piezocomposite ceramics minimize superposition of undesirable modes and increase the bandwidth, as shown in sonograms

Elastografía por ultrasonido: revisión de aspectos técnicos y aplicaciones clínicas. Parte 1

A partir de 1990 comienzan a desarrollarse un conjunto de técnicas cuyo objetivo es evaluar la elasticidad de tejidos blandos mediante ultrasonido. La elastografía por ultrasonido ha aportado una nueva perspectiva a la ecografía proporcionando información para el diagnóstico de diferentes patologías, entre ellas las enfermedades hepáticas, pero con nuevas aplicaciones clínicas en sistema músculo esquelético, mama, tiroides, próstata entre otras. El Laboratorio de Acústica Ultrasonora del Instituto de Física de la Facultad de Ciencias trabaja desde el año 2000 en elastografía por ultrasonido, desarrollando numerosos trabajos experimentales, tesis de maestría y doctorado por lo que cuenta con una amplia experiencia en el tema. En nuestro medio, además de los equipos que permiten realizar elastografía de transición (FibroScan®), se han incorporado en los últimos años ecógrafos con el módulo de elastografía. Particularmente, el Departamento Clínico de Imagenología del Hospital de Clínicas incorporó en 2018/2019 dos ecógrafos que cuentan con elastografía. En este contexto, consideramos importante realizar una actualización y resumen de las distintas técnicas elastográficas, sus ventajas, limitaciones y sus aplicaciones clínicas. El objetivo de este trabajo es realizar una revisión bibliográfica, presentando brevemente las bases físicas y las aplicaciones clínicas de la elastografía en el estudio de patologías hepáticas y mamarias. En una segunda parte de la revisión abordaremos la patología músculo esquelética, tiroides y próstata.ANII: FMV_1_2019_1_15552

Aplicación de elastografía por retorno temporal a la evaluación de textura en quesos

El objetivo de este trabajo fue estudiar la aplicación de la técnica acústica Elastografía por Retorno Temporal (TRE) a la evaluación de la textura de distintos tipos de queso. Se evaluaron ocho muestras comerciales de diferente textura mediante las técnicas de TRE y Análisis de Perfi l de Textura (TPA). Ambas metodologías permitieron detectar diferencias en la textura de las muestras, aportando resultados concordantes. De acuerdo a la regresión de mínimos cuadrados parciales realizada (PLS), el ancho de focalización obtenido por TRE se correlacionó positivamente (R2=0.89) con los parámetros dureza y rigidez del TPA. Esto indica que la técnica de TRE sería un método adecuado para evaluar la textura de los quesos de forma no destructiva. Abstract The aim of this work was to study the application of the acoustic technique Time Reversal Elastography (TRE) for texture evaluation of different types of cheese. Eight commercial cheese samples were evaluated using TRE and Texture Profi le Analysis (TPA). Both methodologies were able to identify differences in the texture of the evaluated cheese samples, providing similar results. According to the partial least squares regression performed, the focalization width determined by TRE was positively correlated (R2=0.89) to hardness and stiffness. This indicates that TRE could be considered as an adequate method for the non destructive evaluation of cheese texture

High frequencies of telomeric associations, chromosome aberrations, and sister chromatid exchanges in ulcerative colitis

Chromosome instability provides a predisposing background to malignancy, contributing to the crucial genetic changes in multistep carcinogenesis. The aim of this work was to analyze chromosome instability in patients with ulcerative colitis (UC) to achieve a better understanding of the increased risk for colorectal cancer. METHODS: Peripheral blood lymphocyte cultures from 20 untreated UC patients and 24 controls were used to study chromosome instability by assessing telomeric associations (TAS), chromosome aberrations (CA), and sister chromatid exchanges (SCE). RESULTS: Mean frequencies of TAS and CA were significantly increased in UC patients compared to controls (p < 0.001). Chromosomes 10, 11, 21, 16, and 19 were the most frequently involved in TAS. A total of 104 CA clustered in 66 breakpoints could be exactly localized. Seven nonrandom bands significantly affected in UC patients were found (p < 0.004), showing a significant correlation with the location of cancer breakpoints (p < 0.003), particularly with colorectal carcinoma rearrangements. SCE analysis showed higher levels in patients compared to controls (p < 0.006), but no differences were observed in cell cycle kinetics. CONCLUSIONS: Our results demonstrate the presence of an unstable genome in UC patients that could be related to the cancer development observed in this disease.Fil: Cottliar, Alejandra. Academia Nacional de Medicina de Buenos Aires. Instituto de Investigaciones Hematológicas "Mariano R. Castex"; ArgentinaFil: Fundia, Ariela Freya. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires. Instituto de Investigaciones Hematológicas "Mariano R. Castex"; ArgentinaFil: Boerr, Luis. Hospital de Gastroenterología “Bonorino Udaondo,; ArgentinaFil: Sambuelli, Alicia. Hospital de Gastroenterología “Bonorino Udaondo,; ArgentinaFil: Negreira, Silvia. Hospital de Gastroenterología “Bonorino Udaondo,; ArgentinaFil: Gil, Anibal. Hospital de Gastroenterología “Bonorino Udaondo,; ArgentinaFil: Gomez, Juan Carlos. Provincia de Buenos Aires. Hospital Interzonal General de Agudos Gral. San Martin; ArgentinaFil: Chopita, Nestor. Provincia de Buenos Aires. Hospital Interzonal General de Agudos Gral. San Martin; ArgentinaFil: Bernedo, Alberto. Provincia de Buenos Aires. Hospital Interzonal General de Agudos Gral. San Martin; ArgentinaFil: Slavutsky, Irma Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires. Instituto de Investigaciones Hematológicas "Mariano R. Castex"; Argentin

Aplicación de elastografía por retorno temporal a la evaluación de textura en quesos

El objetivo de este trabajo fue estudiar la aplicación de la técnica acústica Elastografía por Retorno Temporal (TRE) a la evaluación de la textura de distintos tipos de queso. Se evaluaron ocho muestras comerciales de diferente textura mediante las técnicas de TRE y Análisis de Per l de Textura (TPA). Ambas metodologías permitieron detectar diferencias en la textura de las muestras, aportando resultados concordantes. De acuerdo a la regresión de mínimos cuadrados parciales realizada (PLS), el ancho de focalización obtenido por TRE se correlacionó positivamente (R2=0.89) con los parámetros dureza y rigidez del TPA. Esto indica que la técnica de TRE sería un método adecuado para evaluar la textura de los quesos de forma no destructiva. Palabras clave: Técnicas acústicas, parámetros elásticos, evaluación no destructiva.The aim of this work was to study the application of the acoustic technique Time Reversal Elastography (TRE) for texture evaluation of different types of cheese. Eight commercial cheese samples were evaluated using TRE and Texture Pro le Analysis (TPA). Both methodologies were able to identify differences in the texture of the evaluated cheese samples, providing similar results. According to the partial least squares regression performed, the focalization width determined by TRE was positively correlated (R2=0.89) to hardness and stiffness. This indicates that TRE could be considered as an adequate method for the non destructive evaluation of cheese texture

Publisher Correction : Intensity distribution segmentation in ultrafast Doppler combined with scanning laser confocal microscopy for assessing vascular changes associated with ageing in murine hippocampi

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