30 research outputs found
Application of shear wave propagation to elasticity imaging of biological tissues
Dynamic elastography using ultrasound radiation force is an imaging technique of biological tissues elastic properties. In
a mechanical point of view, biological tissues are supposed isotropic, so their properties are independent of the
reference axis. In these mediums, the tensor of elastic constants can be expressed as a function of two independent
constants : the elastic bulk modulus K (which is linked to the compression wave propagation ) and the elastic shear modulus ÎĽ (which is linked to the shear wave propagation). The development of some cancers can result in weak
variations of the bulk elastic modulus, but can considerably modify the shear elastic modulus. Measurement of m can
then help for the diagnosis of this type of tissue pathology. A judicious mean to measure this parameter is the use of a
non-linear effect called ultrasound radiation force. This force is proportional to the attenuation and the intensity of the
ultrasound beam emitted by the imaging system. This stress source essentially generates a shear wave that propagates
with a velocity proportional to the shear modulus and with a purely transverse polarisation in the far-field (far from the
stress source ). Measurement of the medium displacements induced by shear wave propagation can allow to calculate
the shear modulus of the medium (inverse problem resolution). We performed these measurements from the
radio-frequency (RF) lines obtained with an imaging ultrasound transducer. This work describes precisely the signal
processing realized on the RF lines. This processing is based on the use of a delay estimation method to measure
temporal delays between RF lines during the shear wave propagation. Influence of different parameters (length of the
analyse window, Signal to Noise Ratio of RF lines, sampling frequency, ultrasound transducer characteristics...) on the
measurement precision has been studied. We present displacement curves as a function of time obtained after
optimisation of processing parameters. Experimental results have been favourably compared to a physical model and
allowed us to calculate the shear modulus of the medium.L'élastographie dynamique par force de radiation ultrasonore est une technique d'imagerie des propriétés
élastiques des tissus biologiques. D'un point de vue mécanique, nous supposons que ces milieux sont
isotropes c'est-à -dire que leurs propriétés sont indépendantes du choix des axes de référence. Le tenseur
élastique qui définit les constantes physiques de ce milieu s'exprime en fonction de deux constantes
indépendantes, le module d'élasticité volumique K (qui intervient lors de la propagation des ondes de
compression), et le module d'élasticité de cisaillement μ (qui intervient lors de la propagation des ondes de
cisaillement). L'apparition de certains type de cancers entraîne de faibles variations du module d'élasticité
volumique K, mais peut modifier considérablement le module d'élasticité de cisaillement μ. La mesure de ce
paramètre μ peut ainsi aider au diagnostic de ce type de pathologie des tissus. Un moyen judicieux de mesurer
ce paramètre est d'utiliser un effet non linéaire de force de radiation ultrasonore. Cette force est
proportionnelle à l'atténuation et à l'intensité des ultrasons émis dans le tissu par le système d'imagerie. Cette
source de contrainte génère principalement une onde de cisaillement qui se propage avec une vitesse de
phase proportionnelle au module de cisaillement et une polarisation purement transversale en champ lointain
(loin de la source de contrainte). La mesure des déplacements du milieu, induits par la propagation de cette
onde, peut permettre par résolution du problème inverse de remonter au module de cisaillement. Nous avons
réalisé ces mesures à partir des lignes radiofréquences (RF) obtenues par un transducteur d'imagerie
ultrasonore. Ce travail décrit précisément le traitement que nous avons réalisé sur les lignes RF. Ce traitement
est basé sur l'utilisation d'une méthode d'estimation des retards temporels entre les lignes radiofréquences
obtenues pendant la propagation de l'onde de cisaillement. L'influence de différents paramètres (taille de la
fenêtre glissante d'analyse, rapport signal sur bruit des lignes RF, fréquence d'échantillonnage,
caractéristiques du transducteur ultrasonore...) sur la précision de mesure des déplacements a été étudiée.
Nous présentons les courbes des déplacements en fonction du temps obtenus après optimisation des
paramètres de traitement. Ces résultats expérimentaux ont été favorablement comparés à un modèle
physique et nous ont permis de remonter au module de cisaillement du milieu
L’imagerie ultrasonore de demain : quand les échographes deviennent ultra-rapides
International audienc
Water–air interface deformation by transient acoustic radiation pressure
International audienceThe deformation of a fluid interface by the acoustic radiation pressure has been used for surface tension measurements or to design exotic structures such as acoustic diodes. However, few studies focus on the characterization of the spatial characteristics of deformation induced by transient excitation, making research requiring precise spatial control of deformation challenging. This paper investigates experimentally and numerically the effects of transient excitation on deformation generated by an acoustic radiation pressure at the water–air interface. A numerical model using the finite-element method and based on theoretical background for permanent excitation is generalized to transient excitation. An experimental setup is developed to evaluate the maximum height of interface deformation for different durations and amplitudes of ultrasonic excitation using two complementary methods: the first using a camera and an edge detection algorithm and the other using a multichromatic confocal displacement sensor. Numerical and experimental results for a non-steady-state excitation show a quadratic evolution of the height of deformation as a function of incident pressure and also a linear increase as a function of the excitation duration. The evaluation of the deformation height induced by acoustic radiation pressure at a water–air interface for a transient excitation paves the way to applications requiring noncontact space-time interface modulation, such as subwavelength phenomena
Déformation d’une interface eau-air par la force de radiation acoustique en régime transitoire
Lorsqu’un faisceau acoustique rencontre une interface entre deux milieux d’impĂ©dance diffĂ©rente, la force de radiation acoustique peut induire une dĂ©formation locale de cette interface. Cette force peut ĂŞtre utilisĂ©e pour modifier la gĂ©omĂ©trie de l’interface Ă distance et en temps rĂ©el. Il est alors nĂ©cessaire de connaĂ®tre l’influence des paramètres de contrĂ´le de l’excitation sur les caractĂ©ristiques spatiales de la dĂ©formĂ©e. Cette Ă©tude propose d’identifier et de quantifier l’influence des paramètres d’une excitation transitoire par une approche expĂ©rimentale et numĂ©rique. Un banc de mesure a Ă©tĂ© dĂ©veloppĂ© pour mesurer la hauteur de dĂ©formation d’une interface eau-air en utilisant la force de radiation acoustique. Un transducteur de frĂ©quence centrale Ă©gale Ă 1 MHz, de diamètre 38mm et de distance focale 40mm, est immergĂ© dans l’eau afin de focaliser l’énergie acoustique en incidence normale au niveau de l’interface. Les paramètres de contrĂ´le sont le niveau de pression et la durĂ©e du train d’ondes Ă©mis. La hauteur maximale de la dĂ©formation de l’interface au point focal du transducteur est mesurĂ©e en utilisant deux mĂ©thodes distinctes : i) en utilisant un appareil photo Ă©quipĂ© d’un objectif macro ii) en utilisant un capteur de dĂ©placement laser confocal. En parallèle, un modèle numĂ©rique basĂ© sur la mĂ©thode des Ă©lĂ©ments finis a Ă©tĂ© dĂ©veloppĂ© pour simuler cette dĂ©formation d’interface. Nos rĂ©sultats montrent une Ă©volution non linĂ©aire de la hauteur de la dĂ©formation en fonction de l’amplitude et de la durĂ©e de l’excitation transitoire. Les amplitudes mesurĂ©es sont cohĂ©rentes avec les amplitudes simulĂ©es. Dans le cas par exemple d’un train d’onde de 50 cycles et d’amplitude 2.8 MPa, nous obtenons une dĂ©formation de l’ordre de 300 μ. La mĂ©thode de mesure par le capteur de dĂ©placement confocal permet de suivre l’évolution spatio-temporelle de la dĂ©formation et ouvre de nouvelles perspectives d’étude des surfaces programmables en temps rĂ©el
Investigation of nonlinear bulk viscoelasticity in complex media using dynamic acoustoelasticity
International audienceFew tools have been developed for industrial quality control of textures. The use of contactless techniques, based on acoustic waves, offers an obvious advantage in food-processing industry and cosmetics. The dynamic acoustoelastic testing (DAET) is an acoustic method based on the interaction between a low-frequency compression/expansion pump wave and an ultrasound longitudinal probe wave. This method describes the variations of the bulk viscoelastic modulus, through the quantification of nonlinear elastic and viscous parameters. The DAET method and related model were validated in homogeneous media leading to low values of viscoelastic nonlinearities, essentially governed by the fluid nature. However, the most significant results were obtained in granular or air-based media. The high values of nonlinear viscoelastic parameters are due to the microinhomogeneities of complex media. This method appears to be an interesting alternative to conventional rheometry, especially for the characterization of these complex fluids
Nonlinear acoustic measurements to assess crack density in trabecular bone
International audienc
Contactless deformation of fluid interfaces by acoustic radiation pressure
International audienceReversible and programmable shaping of surfaces promises wide-ranging applications in tunable optics and acoustic metasurfaces. Based on acoustic radiation pressure, contactless and real-time deformation of fluid interface can be achieved. This paper presents an experimental and numerical study to characterize the spatiotemporal properties of the deformation induced by acoustic radiation pressure. Using localized ultrasonic excitation, we report the possibility of on-demand tailoring of the induced protrusion at water-air interface in space and time, depending on the shape of the input pressure field. The experimental method used to measure the deformation of the water surface in space and time shows close agreement with simulations. We demonstrate that acoustic radiation pressure allows shaping protrusion at fluid interfaces, which could be changed into a various set of spatiotemporal distributions, considering simple parameters of the ultrasonic excitation. This paves the way for novel approach to design programmable space and time-dependent gratings at fluid interfaces
Optimised Properties of High Frequency Transducers Based on Curved Piezoelectric Thick Films Obtained by Pad Printing Process
International audienceA high frequency transducer for medical imaging (25 MHz) was fabricated using a pad printing process to deposit a curved lead zirconate titanate (PZT) thick film on electroded backing (porous PZT). This piezoelectric thick film was characterised, and a thickness coupling factor (47%) comparable with that of a bulk ceramic with similar composition was measured. This transducer was successfully modelled with a numerical tool previously published and specifically adapted to curved shapes. The experimental axial and lateral resolutions are 40 and 230 ÎĽm respectively. Moreover, the sensitivity is sufficiently high to consider this transducer to be integrated in an echographic system for high frequency imaging such as skin
Natural shear wave imaging using vocal tract vibrations: Introducing vocal passive elastography (V-PE) to thyroid elasticity mapping
International audienceWe present a shear wave elastography approach for thyroid characterization that is inspired by passive elastography which extracts elasticity from the natural vibrations in living tissues that are caused by cardiac motion, blood pulsatility and muscle activity. On thyroid, this physiological noise is mainly due to the carotid pulsation which is in the 1-10 Hz bandwidth and is located right next to the gland. In order to decrease the shear wavelength and increase the signal to noise ratio, we propose to create in the thyroid a complex shear wave field by using natural vocal tract vibrations. The nature of the sound can be easily modified to be narrow or broad band, with small or large amplitude. Using correlation based algorithm and a sound sustained at 150 Hz, we have developed an innovative technique using ultrasound, allowing us to compute a 2D shear wave velocity map, superposed onto a B-mode ultrasound image of a volunteer's thyroid. Using our Vocal Passive Elastography (V-PE) method, shear wave velocity was measured at every point within a mask surrounding the thyroid with a pixel resolution of 150×150 µm 2. The mean shear wave speed value measured is 3.2 m/s, taking its value from 0.7 m/s to 8.8 m/s. The values obtained were in good agreement with comparative Shear Wave Elastography (SWE) measurements