A comparative study between parallel and normal excitation for crawling wave sonoelastography

Crawling wave sonoelastography (CWS) provides quantitative stiffness information from an examined tissue by the application of two mechanical vibrations that generates an interference pattern which is analyzed to reconstruct a shear wave speed (SWS) image. While CWS performance using parallel excitation setup (PES) has been widely studied in the literature, its implementation is complicated to apply in tissue (i.e. breast,liver) because often requires a normal excitation setup. The aim of this study is to validate the SWS estimation using a normal excitation setup with two different types of coupling attachments for the surface -i.e. surface plate (SP), rounded head (RH)-and perform a quantitative comparison among the three techniques (PES,SP,RH) in homogeneous and heterogeneous gelatin phantoms.The comparison of the three excitation methods was performed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), coefficient of variation (CV) and bias over a range of excitation frequencies.The results in the background (PES:3:74 - 0:14 m/s, SP: 3:43 - 0:14 m/s and RH: 3:32 - 0:07 m/s) and in the inclusion (PES:4:96 - 0:18 m/s, SP: 4:88 - 0:32 m/s and RH: 4:64 - 0:29 m/s) show that both normal excitation setups are comparable to the PES to estimate the SWS. This suggests that this type of setup could be used for ex vivo and in vivo analysis.