Regional-Lag Signed Delay Multiply and Sum Beamforming in Ultrafast Ultrasound Imaging

Ultrafast ultrasound imaging provides very high frame rates but provides poor imaging quality due to unfocused beams. The delay multiply and sum (DMAS) beamformer has been used to improve ultrafast ultrasound imaging contrast but is always accompanied by oversuppression, which produces low-quality speckle images and degrades the contrast performance. A smaller maximum lag in the signed DMAS (sDMAS) contributes better speckle preservation but lower resolution for hyperechoic scatters. To overcome this tradeoff, a regional-lag signed delay multiply and sum (rsDMAS) beamformer is proposed in this article. Innovatively, a region discrimination tool realized by the generalized coherence factor (GCF) is used to limit the maximum lag for spatial coherence estimation. Subaperture coherence smoothing estimates the short-lag coherence instead of multiplication in pairs, thereby reducing calculation complexity and smoothing the speckle texture. Normalization and sign correction are also introduced to achieve better beamforming output. The simulated, phantom, and in vivo data are adopted to evaluate the effectiveness of the proposed beamformer. Numerical results show that the proposed method achieves improvements of the contrast ratio (CR) by 9%, contrast-to-noise ratio (CNR) by 41%, speckle signal-to-noise ratio (sSNR) by 41%, and generalized contrast-to-noise ratio (gCNR) by 0.0004 compared with DMAS (in simulation). Resolution experiments show that the proposed method obtains a loss of 0.07 mm in the full width at half maximum (FWHM) and the same separability of close point scatters as DMAS. These findings indicate that the proposed method achieves higher contrast performance at less obvious sacrifice of the lateral resolution than DMAS.