A Simple, Artifact - Free, Virtual Source Model

Retrospective beamforming is a synthetic technique that, by combination of several converging waves, reduces the number of transmission events without reduction of image quality. However, due to a discontinuity in the conventional spherical virtual source model, an artifact occurs at the focal depth where the virtual sources are located. We correct the artifact by modifying the spherical model by assuming plane wave propagation in a region around the focal depth. This hybrid model is simpler and lighter than the current accepted solution.