Ultrasound Synthetic Aperture Focusing with the Delay Multiply and sum beamforming algorithm.

The Delay Multiply and Sum (DMAS) beamforming algorithm was originally conceived for microwave imaging of breast cancer. In a previous work, we demonstrated that, by properly modifying and improving the algorithm processing steps, DMAS can be successfully applied to ultrasound signals for B-mode image formation and that it outperforms standard Delay and Sum (DAS) beamforming in terms of contrast resolution. As previously pointed out, however, DMAS-beamformed B-mode images, in which fixed and dynamic focusing are applied respectively during transmit and receive operations, show an intensity drop away from the transmit focal depth compared to DAS images. This could be due to the fact that DMAS beamforming is based on a measure of backscattered signal coherence, which reaches its maximum only at the transmit focus, where signals are perfectly realigned. The preliminary results presented in this work show that, by employing Synthetic Aperture Focusing (SAF), which allows to achieve dynamic focusing both on transmission and reception, this intensity loss is compensated, as DAS and DMAS images have almost the same maximum amplitude level at all depths.