Ultrasound Strain Imaging With Null Subtraction and Coded Plane Waves

Accurate displacement estimation is central to ultrasound strain imaging (USI), which provides a full description of a 2-D/3-D deformation field to infer elasticity and detect tissue abnormalities. However, lateral displacement estimation has been the major bottleneck, especially with high frame rate requirements, due to inferior spatial resolution, low sampling, and the lack of phase information in that direction. This study focuses on enhancing lateral displacement estimation by improving the lateral resolution of ultrasound multiangle plane-wave imaging through a nonlinear beamformer, incoherent compounding (IC) null subtraction imaging (NSI). While IC-NSI effectively reduces both mainlobe width and secondary lobe levels, its limited penetration depth and reduced speckle coherence are detrimental to tissue motion estimation. We hereby propose to improve the signal-to-noise ratio (SNR) and thus the penetration depth by integrating cascaded dual-polarity wave (CDW) into IC-NSI. We evaluate the feasibility and performance of IC-NSI, with and without CDW, for tissue displacement estimation through Field II and COMSOL simulations of deforming tubes, phantom experiments, and an in vivo study of the human common carotid artery. Both in silico and in vivo carotid ultrasound images obtained by the proposed method exhibited ~40% improvement in lateral resolution compared with those by coherent plane-wave compounding (CPWC). In phantom experiments, the sonographic SNR improved by 14-17 dB across depths of 20-40 mm and had a 32% reduction in mean absolute error (MAE) in lateral motion estimation in a controlled linear translation scenario. In simulations, our method achieved 13% higher estimation accuracy in lateral displacement under varying strain conditions compared to CPWC. These results demonstrated the conceptual and computational simplicity of the proposed method for high-quality USI of thin biological structures.