Simulation of nonlinear ultrasound propagation in heterogeneous tissue

A numerical model was proposed for the simulation of the nonlinear ultrasound propagation in heterogeneous tissue. First, the coupled nonlinear wave equations for pressure and velocity were obtained based on 1-st order nonlinear wave equations in soft tissue to reduce the complexity of numerical computation. Then, k-space method was used to solve the derived nonlinear wave equations to reduce the memory usage and the computation time of the simulation, while preserving the computation accuracy. Compared with the analytic solution of a 1-dimensinal problem and the finite-different time-domain (FDTD) results of a 2-dimensinal problem, and the accuracy of the proposed model was validated. With grid size of 1/9 of the wavelength and Courant-Friedrichs-Lewy (CFL) of 0.3, the square errors of the proposed model and the FDTD method are 0.0125% and 42.5%, respectively. Medical harmonic ultrasound imaging was simulated using the proposed method based on a digital human abdominal map. The results show that image quality can be improved in the deeper tissue by using the harmonic signal. © 2016, Zhejiang University Press. All right reserved.