Abstract

Nonlinear Regimes of Lesion Formation by HIFU in Tissue-Mimicking Phantom

V.A.Khokhlova (Department of Acoustics, Faculty of Physics, Moscow State University, Moscow, Russia); P.J.Kaczkowski, B.W.Cunitz, M.R.Bailey, L.A.Crum (Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA)

e-mail: vera@acs366b.phys.msu.su

Nonlinear effects of high intensity focused ultrasound (HIFU) on the dynamics of thermal lesion formation were investigated experimentally and numerically. Simulations were performed using a KZK model for the acoustic field combined with the bioheat equation. Transparent polyacrylamide gel was used in experiments as a tissue-mimicking phantom. Various regimes of treatment were studied based on an equal amount of ultrasound energy radiated into the gel by a 3.5 MHz single element transducer with 23 mm diameter and 35 mm radius of curvature. Single lesions were produced, and lesion stripes were obtained by moving the ultrasound transducer. For single lesions, variation of acoustic pressure amplitude was combined either with the same exposure time and different duty cycle or with different exposure times in the continuous wave (cw) regime. For lesion stripes, variation of acoustic pressure amplitude was combined either with the same transducer velocity and different duty cycle or with different transducer velocity in the cw regime. Substantial increase of the lesion size was observed with high-amplitude waves, which was hypothesized to be due to both acoustic nonlinearity and enhanced cavitation. Further experiments were performed with different frequency (2 and 4 MHz) and elevated hydrostatic pressure (1 - 100 bars) to separate cavitation and nonlinear distortion mechanisms. Work was supported by NASA/NSBRI, NSF, CRDF, RFBR, and NIH.

Section : 5