Synthetic transmit aperture beamforming for sound velocity estimation using channel-domain differential phase gradient

Abstract

In ultrasound array imaging system, degradation of image quality occurs due to mismatch between beamforming sound velocity and tissue sound velocity. Channel-domain differential phase gradient has been previously proposed to optimize the beamforming sound velocity but its efficacy is limited to transmit focal depth. This is due to the low spatial coherence of channel signal in the non-focal region which leads to over-estimation of beamforming sound velocity. In order to alleviate the estimation bias of beamforming sound velocity, synthetic transmit aperture beamforming is proposed in this study to maintain the spatial coherence of channel data over the entire image depth. Specifically, channel signals from adjacent scanlines are combined to remedy the focusing quality in the non-focal region and then the zero of differential phase gradient between the left and right sub-apertures after depth and scanline averaging determines the optimal sound velocity. Results indicate that the synthetic transmit aperture beamforming effectively reduces the estimation bias of beamforming sound velocity from 4.3 % to 0.1 % in the simulations and from 8.8 % to 0.1 % in ATS phantom measurement. Both the contrast ratio of the cyst region and the lateral resolution of wire reflector both peak when the optimized sound velocity is utilized for beamforming. Compared to our previous work, the improved method also exhibits higher robustness of sound velocity estimation in the presence of strong random noises.