Abstract (Invited)

Effect of Cavitation on Ultrasound Absorption in Biological Tissue

J.Y.Chapelon, S.Pichardo, F.Chavrier, L.Curiel, Y.C.Angel (INSERM U556, Lyon, France)

e-mail: chapelon@lyon151.inserm.fr

In biological tissue, the application of a high intensity ultrasound field often gives rise to acoustic cavitation. The presence of even small concentrations of bubbles not only increases tissue compressibility, which reduces sound speed, but also causes dispersion and attenuation. In addition, the nonlinearity due to bubble resonance can exceed, by orders of magnitude, the intrinsic nonlinearity due to the medium itself. These effects have been observed during therapeutic focused ultrasound, where cavitation bubbles formed in the propagation path may cause a displacement of the lesion toward the transducer. Our approach to quantify this enhanced absorption is to consider the bubble acoustic radiation mechanism calculated from a Rayleigh-Plessey equation in order to estimate a nonlinear .global attenuation coefficient. of the tissue with cavitation bubbles. An alternative approach is to adopt the model of Zabolotskaya and Soluyan, which is based on the assumption that bubbles provide the dominant source of nonlinearity. With this model, the nonlinearity is again taken into account by a Rayleigh-Plessey equation and the KZK equation is used to calculate ultrasound propagation in the tissue with cavitation bubbles. These two approaches will be presented and discussed in the context of typical situations observed during focused ultrasound surgery.

Section : 5