Influence of the delay-multiply-and-sum beamformer on the ultrasound image amplitude

The Delay-Multiply-And-Sum (DMAS) beamformer has recently been presented in the context of medical ultrasound image formation. Images obtained with the DMAS beamformer present improved contrast resolution and noise rejection when compared to images obtained with the standard Delay-And-Sum (DAS) beamformer. We study here the signal statistics for a homogeneous medium using both the DAS and DMAS beamformers. We show that they are dependent on the coherence between the received signals. The final image amplitude is more dependent on the signal coherence when using the DMAS beamformer than when using the DAS beamformer. Ultrasound images of a phantom illustrate the dependency of the image amplitude with the signal coherence when using the DMAS beamformer. We conclude that the improved image quality obtained using the DMAS beamformer comes from a larger signal amplitude suppression as the signal coherence decreases.