Bias voltage modulation methods and its optimization for nonlinear contrast imaging

Congrès sous l’égide de la Société Française de Génie Biologique et Médical (SFGBM).National audienceThe main difficulty in applying ultrasound contrast imaging techniques with cMUT probe comes from the intrinsic nonlinearity of the transducer itself. An approach has been developed in order to adapt the amplitude modulation techniques (AM) to cMUTs. Bias Voltage Modulation (BVM)[1] allows a complete cancellation of the echoes from linear reflectors and thus an enhancement of the contrast agent detection. The main limit is that it can only be applied with low bias voltage, far from the maximum of the probe sensitivity (i.e. at the collapse). Here is proposed an optimization of the BVM sequence allowing a good compensation of cMUT intrinsic nonlinearity even at high bias voltages

Pulsed bi-frequency method for characterization of microbubbles in the context of decompression sickness

International audienceDuring hyperbaric decompression, the absolute ambient pressure is reducing; microbubbles may be generated from pre-existing gas nuclei. An accurate monitoring of the size and of the density of the bubble population will provide a valuable means to understand the nucleation and growth processes in tissues. In this aim, an ultrasonic characterization method based on a dual frequency technique applied on a single bubble is tested. The method consists in sending two ultrasonic waves on a stationary bubble. One is a low frequency wave (30 kHz\leqflf\leq 60 kHz), which excites the bubble near its resonance frequency and the other is a high frequency (fhf=1MHz) wave that measures the changes in the acoustic cross-section induced by the low frequency activation. The resonance frequency, directly related to the radius, can be detected by looking at the spectrum. The development of an optimal sensor embedded on a diver leads to the use of a single transducer acting as an transmitter/receiver of pulsed waves. The straight forward outcome is a higher probability detection and a better radius estimation accuracy. Distinctions in the signal processing allows dedicated detection/sizing processes suitable either for bubbles circulating in the blood flow (larger bubble) or for stationary bubbles in tissues (several microns)

Detection and characterization of microbubbles : application to the prevention of decompression sickness.

Les accidents de désaturation (ADD) résultent de la formation de microbulles dans les tissus lors de la décompression. De nombreux corps de métiers sont concernés par cette problématique : plongeurs, astronautes, tunneliers, personnel médical hyperbare... On observe que ces accidents peuvent survenir alors même que les tables de décompression sont respectées. La détection et la caractérisation des bulles de décompression présentent un intérêt diagnostic potentiel pour la prévention des ADD. Aujourd’hui, la détection de microbulles est réalisée par des personnels de santé expérimentés en utilisant des systèmes Doppler. Cependant, cette approche présente une grande dépendance à l'opérateur et ne permet pas d'obtenir une information quantitative (nombre, taille) sur la distribution des bulles circulantes. Par ailleurs, elle n'est pas adaptée à la détection de bulles tissulaires.Ces limitations conduisent à mettre en oeuvre une méthode ultrasonore bifréquentielle de détection et de caractérisation par mise en résonance des microbulles. Les contraintes de mesure temps-réel, de polydispersité en taille ([1 à 200 μm]) et de sursaturation des tissus imposent d'utiliser des ondes d'excitation de très faibles puissances mais très large bande.Les solutions mises en oeuvre visent d'une part à réduire la complexité de l'instrumentation et d'autre part à prendre en considération la dynamique de l'excitation. Par ailleurs, une solution originale, ayant fait l’objet d’un dépôt de brevet, est développée. Elle permet de s'affranchir de la mise en résonance tout en conservant un caractèrediscriminant séparant bulles et tissus.Decompression sicknesses (DCS) are a consequence of microbubbles formation in tissues during decompression. Many fields are affected by this issue: divers, astronauts, tunneling, hyperbaric medical staff... It is observed that these accidents can occur even if the decompression tables are respected. The detection and characterization of decompression bubbles have a diagnostic potential for the prevention of DCS. Today, the detection of microbubbles is performed by experienced health workers using Doppler systems. However, this approach has a high dependence on the operator and does not provide quantitative information (number, size) about the distribution of circulating bubbles. Moreover, it is not suitable for the detection of stationary bubbles (tissue bubbles).These limitations lead to the development of a bi-frequency ultrasonic method for microbubbles detection and characterization by setting them into resonance. The constraints as real-time measurements, size polydispersity ([1 to 200 μm]) and saturation of tissues require the use of very low powerful excitation but high bandwidth waves.The solutions implemented are aimed firstly to reduce the complexity of the instrumentation and secondly to consider the dynamics of the excitation. In addition, an original solution, protected by a patent, has been developed. It allows to overcome the measurement of resonance while maintaining a discriminating character between bubbles and tissues

Monitoring microbubbles’ dynamics using a dual modulation method

International audienceAn experimental method for characterizing microbubbles' oscillations is presented. With a Dual Frequency ultrasound excitation method, both relative and absolute microbubble size variations can be measured. Using the same experimental setup, a simple signal processing step applied to both the amplitude and the frequency modulations yields a two-fold picture of microbubbles' dynamics. In addition, assuming the occurrence of small radial oscillations, the equilibrium radius of the microbubbles can be accurately estimated

Caractérisation ultrasonore de l’évolution de la texture de matrices laitières lors de différentes transformations physico-chimiques industrielles

L’industrie laitière est en recherche continue de techniques de suivi de texture pour aider au pilotage de la fabrication des produits laitiers. C’est en effet un secteur où on observe une variabilité importante des matières premières (provenance géographique, saisonnalité), où les transformations biochimiques sont complexes et les attentes des consommateurs en termes de texture très fortes. Pourtant il n’existe que très peu d’instrument en ligne. Compte tenu de leur caractère non destructif, non invasif et temps réel, les technologies ultrasonores se révèlent une alternative prometteuse pour répondre à ces besoins de contrôle en ligne de texture. Dans ce contexte, différentes transformations laitières ont été suivies par une méthode de spectroscopie ultrasonore en transmission. L’approche a montré une très bonne sensibilité pour suivre la remontée des matières grasses lors d’une cinétique de crémage, ainsi qu’un processus de concentration en lait reconstitué. La méthode a ensuite été appliquée à des coagulations de type présure et acide. Ces deux types de coagulation ont montré des cinétiques différentes, précieuses pour les suivis en production. Après correction des effets de température, des temps de prise caractéristiques des transitions de phases ont pu être détectées. Enfin, nous avons pu suivre un phénomène de cristallisation dans le beurre, avec une signature ultrasonore intéressante, déjà observée dans d’autres formes de cristallisation comme le chocolat

Microbubble-mediated ultrasound drug-delivery and therapeutic monitoring

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Acoustic and Elastic Properties of a Blood Clot during Microbubble-Enhanced Sonothrombolysis: Hardening of the Clot with Inertial Cavitation

International audienceStroke is the second leading cause of death worldwide. Existing therapies present limitations, and other therapeutic alternatives are sought, such as sonothrombolysis with microbubbles (STL). The aim of this study was to evaluate the change induced by STL with or without recombinant tissue-type plasminogen activator (rtPA) on the acoustic and elastic properties of the blood clot by measuring its sound speed (SoS) and shear wave speed (SWS) with high frequency ultrasound and ultrafast imaging, respectively. An in-vitro setup was used and human blood clots were submitted to a combination of microbubbles and rtPA. The results demonstrate that STL induces a raise of SoS in the blood clot, specifically when combined with rtPA (p < 0.05). Moreover, the combination of rtPA and STL induces a hardening of the clot in comparison to rtPA alone (p < 0.05). This is the first assessment of acoustoelastic properties of blood clots during STL. The combination of rtPA and STL induce SoS and hardening of the clot, which is known to impair the penetration of thrombolytic drugs and their efficac

Tunable microbubble generator using electrolysis and ultrasound

This letter reports on a method for producing on demand calibrated bubbles in a non-chemically controlled solution using localized micro-electrolysis and ultrasound. Implementing a feedback loop in the process leads to a point source of stable mono-dispersed microbubbles. This approach overcomes the inertial constraints encountered in microfluidics with the possibility to produce from a single to an array of calibrated bubbles. Moreover, this method avoids the use of additional surfactant that may modify the composition of the host fluid. It impacts across a broad range of scientific domains from bioengineering, sensing to environment

Evaluation of high resolution ultrasound as a tool for assessing the 3D volume of blood clots during in vitro thrombolysis

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