Abstract
Tissue biomechanical properties are known to be sensitive to pathological changes. Accordingly, various techniques have been developed to estimate tissue mechanical properties. Shear-wave elastography (SWE) measures shear-wave speed (SWS) in tissues, which can be related to shear modulus. Although viscosity or stress-strain non-linearity may act as confounder of SWE, their explicit characterization may also provide additional information about tissue composition as a contrast modality. Viscosity can be related to frequency dispersion of SWS, which can be characterized using multi-frequency measurements, herein called spectral shear-wave elastography (SSWE). Additionally, non-linear shear modulus can be quantified and parameterized based on SWS changes with respect to applied stress; a phenomenon called acousto-elasticity (AE). In this work, we characterize the non-linear parameters of tissue as a function of excitation frequency by utilizing both AE and SSWE together. For this, we apply incremental amounts of quasi-static stress on a medium, while imaging and quantifying SWS dispersion via SSWE. Results from phantom and ex-vivo porcine liver experiments demonstrate the feasibility of measuring frequency-dependent non-linear parameters using the proposed method. SWS propagation in porcine liver tissue was observed to change from 1.8 m/s at 100 Hz to 3.3 m/s at 700 Hz, while increasing by approximately 25% from a strain of 0% to 12% across these frequencies. Index terms-Ultrasound, elastography, acousto-elasticity, tissue non-linearity, shear-wave dispersion.
Otesteanu, Corin F