laboratoire de physique statistique
 
 
laboratoire de physique statistique

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 


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2012
A model for ultrasound absorption and dispersion in dilute suspensions of nanometric contrast agents - Coulouvrat, Francois and Thomas, Jean-Louis and Astafyeva, Ksenia and Taulier, Nicolas and Conoir, Jean-Marc and Urbach, Wladimir
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1323748-3759 (2012)

Abstract : Ultrasound dispersion and absorption are examined in dilute suspensions of contrast agents of nanometric size, with a typical radius around 100 nm. These kinds of contrast agents are designed for targeted delivery of drugs for cancer treatment. Compared to standard contrast agents used for imaging, particles are of smaller size to pass through the endothelial barrier, their shell, made up of biocompatible polymer, is stiffer to undergo a longer lifetime, and they have a liquid core instead of a gaseous one. Ultrasound propagation in dilute suspension is modeled by combining two modes for particle oscillations. The first one is a dilatational mode assuming an incompressible shell with a rheological behavior of Kelvin-Voigt or Maxwell type. The second one is a translational mode induced by visco-inertial interaction with the ambient fluid. The relative importance of these two modes of interaction on both dispersion and absorption is quantified and analyzed for a model system and for two radii (75 and 150 nm) and the two rheological models. The influence of shell parameters (Young modulus, viscosity, and relative thickness) is finally discussed. (C) 2012 Acoustical Society of America. [http://dx.doi.org/10.1121/1.4765639]
 
2011
Two-dimensional simulation of linear wave propagation in a suspension of polymeric microcapsules used as ultrasound contrast agents - Haiat, Guillaume and Berti, Romain and Galaz, Belfor and Taulier, Nicolas and Amman, Jean-Jacques and Urbach, Wladimir
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1291642-1652 (2011)

Abstract : A generation of tissue-specific stable ultrasound contrast agent (UCA) composed of a polymeric capsule with a perfluorocarbone liquid core has become available. Despite promising uses in clinical practice, the acoustical behavior of such UCA suspensions remains unclear. A simulation code (2-D finite-difference time domain, FDTD) already validated for homogeneous particles [Galaz Haiat, Berti, Taulier, Amman and Urbach, (2010). J. Acoust. Soc. Am. 127, 148-154] is used to model the ultrasound propagation in such UCA suspensions at 50 MHz to investigate the sensitivity of the ultrasonic parameters to physical parameters of UCA. The FDTD simulation code is validated by comparison with results obtained using a shell scatterer model. The attenuation coefficient (respectively, the sound velocity) increases (respectively, decreases) from 4.1 to 58.4 dB/cm (respectively, 1495 to 1428 m/s) when the concentration varies between 1.37 and 79.4 mg/ml, while the backscattered intensity increases non-linearly, showing that a concentration of around 30 mg/ml is sufficient to obtain optimal backscattering intensity. The acoustical parameters vary significantly as a function of the membrane thickness, longitudinal and transverse velocity, indicating that mode conversions in the membrane play an important role in the ultrasonic propagation. The results may be used to help manufacturers to conceive optimal liquid-filled UCA suspensions. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3543966]
 
2010
Experimental validation of a time domain simulation of high frequency ultrasonic propagation in a suspension of rigid particles - Galaz, Belfor and Haiat, Guillaume and Berti, Romain and Taulier, Nicolas and Amman, Jean-Jacques and Urbach, Wladimir
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 127148-154 (2010)

Abstract : Ultrasonic propagation in suspensions of particles is a difficult problem due to the random spatial distribution of the particles. Two-dimensional finite-difference time domain simulations of ultrasonic propagation in suspensions of polystyrene 5.3 mu m diameter microdisks are performed at about 50 MHz. The numerical results are compared with the Faran model, considering an isolated microdisk, leading to a maximum difference of 15\% between the scattering cross-section values obtained analytically and numerically. Experiments are performed with suspensions in through transmission and backscattering modes. The attenuation coefficient at 50 MHz (alpha), the ultrasonic velocity (V), and the relative backscattered intensity (I(B)) are measured for concentrations from 2 to 25 mg/ml, obtained by modifying the number of particles. Each experimental ultrasonic parameter is compared to numerical results obtained by averaging the results derived from 15 spatial distributions of microdisks. alpha increases with the concentration from 1 to 17 dB/cm. IB increases with concentration from 2 to 16 dB. The variation of V versus concentration is compared with the numerical results, as well as with an effective medium model. A good agreement is found between experimental and numerical results (the larger discrepancy is found for alpha with a difference lower than 2.1 dB/cm ). (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3270399]