Comparison of qualitative and quantitative acoustic radiation force based elasticity imaging methods

Acoustic radiation force based elasticity imaging methods utilize focused acoustic beams to mechanically excite tissue and ultrasonic correlation based methods to monitor the dynamic response of the tissue, which reflects the underlying tissue stiffness. Both qualitative images and quantitative images can be derived depending upon the selected beam sequences and data processing algorithms. Qualitative images provide good spatial resolution and contrast, but reflect only relative differences in tissue stiffness. Quantitative measurements of tissue stiffness can be obtained by measuring the speed of propagating shear waves induced in tissue by acoustic radiation force. In homogeneous media, time-of-flight (TOF) measurements of shear wave speed (SWS) ideally are independent of the size of the region of interest (or reconstruction kernel), thus extensive averaging can be performed to improve estimate accuracy and precision. However, in heterogeneous media, shear wave morphology is altered by discontinuities in stiffness due to reflections or boundary conditions which introduce error to the measured SWS. In addition, the size of the reconstruction kernel limits the spatial resolution, or ability to precisely localize changes in stiffness. This study investigates the impact of: arrival time estimation method, shear wavelength, and reconstruction kernel size on the accuracy and spatial resolution of TOF SWS reconstruction in heterogeneous media using finite element method (FEM) simulations.