Delay-Multiply-and-Sum Beamforming with Transmit Minimum-Variance Estimation in Multi-Angle Plane-Wave Imaging

For multi-angle plane-wave (PW) imaging, Delay-Multiply-and-Sum (DMAS) beamforming has been used to improve the image resolution and contrast by introducing signal coherence into the image display. Signal coherence can be extracted in the dimension of either PW transmit angle (Tx) or receive channel (Rx). Nonetheless, excessive signal coherence may compromise the speckle quality and thus degrade the contrast-to-noise ratio (CNR). In this study, minimum-variance (MV) estimation is combined with DMAS beamforming to increase the image resolution without excessive signal coherence while the background speckle quality is better maintained. In the proposed Tx-MV-DMAS beamforming, low-resolution images are firstly constructed for all available PW transmit angles to generate the transmit vector. After magnitude-scaling the transmit vector by p-th root while maintaining the phase, the MV weighting is adaptively estimated for each image pixel and then the high-resolution image is produced by weighted summation of the transmit vector. Finally, the magnitude of the high-resolution image is restored by p-th power to introduce the signal coherence in DMAS beamforming. PICMUS simulation and vivo data are used to compare the performance of Tx-MV-DMAS with the conventional Tx-DMAS and CPWC.B-mode images show that the Tx-MV-DMAS offer significant improvements over Tx-DMAS in terms of image resolution and contrast while the background speckle remains visually comparable.