Generalization of the iterative nonlinear contrast source method to realistic, nonlinear biomedical tissue

Originally, the iterative nonlinear contrast source (INCS) method has been developed to compute the nonlinear, wide‐angle, pulsed ultrasound field in a homogeneous and lossless medium. The method considers the nonlinear term of the lossless Westervelt equation as a distributed contrast source in a linear background medium. The full nonlinear wave field follows from the Neumann iterative solution of the resulting integral equation. Each iteration step involves the spatiotemporal convolution of the background Green’s function with an estimate of the contrast source. Appropriate filtering provides accurate field predictions for a discretization approaching two points per smallest wavelength or period. The current paper first discusses the theoretical generalization of the original contrast source approach, e.g., to include tissue attenuation or inhomogeneity. Next, computational results are presented that show the directional independence (even for the nonlinear distortion) and the wide‐angle performance of the original INCS method. Finally, results are presented for extensions that can deal with power law losses or inhomogeneity in the wave speed. The wide‐angle capability and the versatility of the contrast source approach demonstrate that the INCS method is well‐suited for modeling the various aspects of realistic biomedical tissue behavior. [Work supported by STW and NCF.]