Fast shear compounding using directional filtering and two-dimensional shear wave speed calculation

Shear compounding illuminates the shear wave imaging field with differently angled shear waves from which elasticity maps can be reconstructed and compounded to increase SNR and contrast. However, the shear imaging frame rate may be reduced by the need for multiple separate generations and detections of the differently angled shear waves. To preserve frame rate and increase efficiency of shear compounding, this study proposes a fast shear compounding method by producing multiple shear waves with different angles at different spatial locations simultaneously to obtain a full field-of-view (FOV) two-dimensional (2D) compounded shear elasticity map with only one push and detection cycle. A 2D shear wave speed calculation method was developed to accurately measure the speed of angled shear wave propagation. A robust estimation method proposed by Anderssen-Hegland was adapted to improve the smoothness of local shear wave speed estimation while preserving the spatial resolution. A multi-directional filter was designed to fit each propagation direction of shear waves. A final shear wave speed map could be obtained by compounding shear wave speed maps reconstructed from all directions. An inclusion phantom experiment showed a smooth compounded shear wave speed map with three types of inclusions resolved with sharp boundaries and good contrast to the background. Results showed good agreement between the measured inclusion stiffness and nominal values. These results indicate that the proposed shear compounding method is effective in providing compounded shear elasticity maps with a large FOV and good contrast while preserving a high shear wave imaging frame rate.