Simulation of focusing high intensity ultrasound by time reversal method

Numerical simulations are used to investigate the validation of using time reversal to focus sound beams in high intensity ultrasound. Time reversal is a method based on linear and lossless sound field. But the high intensity of HIFU sound field brings with high nonlinearity and body tissues brings with thermoviscous absorption. So it is necessary to investigate whether time reversal is feasible in focusing sound beams in HIFU, whether it is preferable to normal methods. Nonlinearity and absorption is considered in numerical simulation based on KZK nonlinear parabolic wave equation. A time-domain algorithm with two-dimensional finite difference is used to solve the equation. Layered biological tissue model is created. Numerical results with various parameters are calculated to investigate the influence of nonlinearity and absorption on time reversal results respectively. Moreover, results are calculated both using time reversal and phased array method, to compare the differences on beam focusing behavior. It is founded that thermoviscous absorption has less effect on time reversal, while the influence of nonlinearity is greater. It is shown that in the presence of nonlinearity and thermoviscous absorption in HIFU, the ability of time reversal to focus the sound beams is also robust. Comparison results are shown that time reversal method is more accurate than normal method in inhomogeneous media considering nonlinearity and thermoviscous absorption. So time reversal method has a great prospect to focus sound beams in HIFU.