Adaptive optimization of ultrasound beamforming sound velocity using sub-aperture differential phase gradient

Ultrasound array imaging systems rely on a presumed beamforming sound velocity to calculate the time compensation of each element for receive focusing. The mismatch between the tissue sound velocity and the beamforming sound velocity can degrade the focusing quality due to loss of phase coherence. Since the tissue sound velocity cannot be known in prior, an adaptive optimization of beamforming sound velocity is required to improve the image quality. Differential phase gradient of channel data is proposed to estimate the optimal sound velocity for beamforming. The sound velocity optimization is achieved when the differential phase gradient between the left and the right sub-apertures approaches zero. Channel-domain autocorrelation is utilized for the estimation of phase gradient due to its high rejection to noise interference and low computational complexity. Results indicate that, compared to the conventional phase variance method, the proposed differential phase gradient reduces the standard deviation of sound velocity estimation from 0.5% to 0.2% while the accuracy remains comparable. The contrast ratio of the cyst region achieves the peak when the optimized sound velocity is utilized for beamforming. The lateral resolution of point target also improves by 14.3% after sound velocity optimization. The proposed method increases the robustness of sound velocity optimization. It is suggested to be implemented at transmit focal depth and without beam steering for better performance.