Performance study of the Iterative Nonlinear Contrast Source method

Abstract

The computation of nonlinear, pulsed acoustic fields in three‐dimensional, large‐scale (100λ×100λ×100λ) configurations becomes increasingly important in e.g. biomedical ultrasound. Current methods either suffer from approximations which favor a specific direction of propagation, or yield prohibitively large grids in case of large computational domains. To overcome such limitations, the Iterative Nonlinear Contrast Source (INCS) method has been developed. The INCS method considers the nonlinear term in the Westervelt equation to describe a distributed contrast source that causes the nonlinear distortion of the acoustic field. Both the contrast source and the nonlinear field are successively updated using Neumann iteration. This paper focuses on three performance aspects of the INCS method: the directional independence, the possibility to restrict the domain of the nonlinear contrast source, and the ability to deal with an off‐axis beam. The latter issue includes a comparison with the AS‐NLP method. The results prove that the INCS method is directionally independent. It is also shown that the contrast source domain may often be reduced in size, which in turn may lead to less numerical effort for the iterations. Moreover, the deviation of the results of the INCS method and the AS‐NLP method displays the difficulty of the latter method to deal with off‐axis nonlinear propagation.