The Simulation of strongly focused finite amplitude ultrasound and temperature field

This paper simulates the temperature field generated by a high intensity focused ultrasound (HIFU) in a tissue-like material. The linear and nonlinear HIFU field are predicted respectively by solving the linear and nonlinear spherodial beam equations (SBE) using frequency domain method. And the temperature field is simulated by solving the “bioheat equation” with the finite-difference time-domain (FDTD) method. Because the spherodial beam equation can reliably applied to predict the HIFU field excited by a wider aperture angle transducer (for half-aperture angles of up to 40°), we simulate the heat pattern generated by the HIFU field with various half-aperture angles (10°, 20°, 30°, 40°). Numerical results reveal the nonlinearity of ultrasound field play crucial roles in the generation of temperature field. The peak temperature at focus predicted by a nonlinear equation field is evidently higher than that predicted by a linear equation especially when the aperture angle is wide because of the strongly absorption of the higher-frequency harmonics. The excess heat increases with the increase of the aperture angle and becomes significant large when the halfaperture angle is up to 40°.