Null subtraction imaging combined with modified delay multiply-and-sum beamforming for coherent plane-wave compounding.

Coherent plane-wave compounding, while efficient for ultrafast ultrasound imaging, yields lower image quality due to unfocused waves. Delay multiply-and-sum (DMAS) beamformer is one of the representative coherence-based methods which can improve images quality, but suffers from poor speckle quality brought by oversuppression. Current DMAS-based methods involve trade-offs between contrast, resolution, and speckle preservation. To overcome this limitation, a new beamformer method combining the null subtraction imaging (NSI) and DMAS is investigated. The proposed method explores the DMAS on different beamformers which employs NSI and delay and sum (DAS) at receive and do multiply-and-sum on different beamformers across transmitting dimension, thereby simultaneously possessing the speckle quality of DAS and the high resolution of NSI. The effectiveness of the proposed method is evaluated through simulation, phantom, and in vivo datasets. From the experimental study, in comparison with NSI, the proposed method has improved contrast ratio by 10.02%, speckle signal-to-noise ratio by 45.19%, and generalized contrast-to-noise ratio by 12.37%. The method has also improved the full width at half maximum by up to 0.24 mm. The results indicate that the proposed method achieves better resolution and contrast, while also alleviating the issue of excessive compression.