Simulation of temperature fields in soft tissue caused by nonlinear propagation of ultrasound pulses

Nonlinear propagation of ultrasound causes increased heating in tissue. This occurs because nonlinear distortions of the ultrasound wave in the course of its propagation pump energy into higher-frequency harmonics which are absorbed more strongly than the fundamental. This process remains little investigated so far. The aim of our work is to investigate numerically the effect of nonlinear propagation of ultrasound waves on temperature rise in soft tissue, taking into account that higher harmonics have higher absorption coefficients. To this end, a numerical code has been developed that couples the modeling of nonlinear ultrasound propagation and the modeling of temperature elevations produced by this propagation. It has been shown that neglecting the fact that higher harmonics are absorbed more strongly than the fundamental results in a considerable underestimation of temperature rise.