Computation of three-dimensional, pulsed, nonlinear acoustic wavefields from medical phased array transducers in very large domains

Abstract

For the optimization and development of medical ultrasound transducers and imaging modalities, the Iterative Nonlinear Contrast Source (INCS) method has been developed. This numerical method predicts the nonlinear acoustic pressure field, generated by a pulsed, plane source with an arbitrary aperture, and propagating in a three-dimensional tissue-like medium that extends over a very large domain of interest. The INCS method obtains the acoustic pressure from the nonlinear acoustic wave equation by treating the nonlinear term as a contrast source. The full nonlinear wave field is then found by iteratively solving the linearized wave problem using a Green's function method. By employing the Filtered Convolution method discussed in a companion paper, accurate field predictions are obtained at a discretization approaching two points per wavelength or period of the highest frequency of interest. In this paper, very large-scale, nonlinear field profiles are presented for transducers with cylindrical as well as phased array geometries, excited with a pulsed waveform having a center frequency of 1-2 MHz. Comparison with results obtained from models of reduced complexity shows that in all cases the INCS method accurately predicts the nonlinear field. [Work supported by STW and NCF.]