Ultrasound Shear Wave Attenuation Estimates are Sensitive to In situ Fluid Content: In vitro and Ex vivo Studies

In shear wave elastography, viscoelastic properties of tissues can be estimated by fitting a rheological model to the phase velocity dispersion curve. However, there is a lack of consensus on the model that best represents tissue behavior. Model-free elastography approaches based on shear wave attenuation (SWA) and dispersion slope analysis have been reported previously. This study evaluated the ability of SWA and dispersion slope analysis to assess fluid content in situ using viscoelastic phantoms and ex vivo chicken breast. Model-free parameters were estimated in viscoelastic phantoms (with fluid percentages ranging from 72.6% to 79.9%, and pre- and post-compression by 10%) and ex vivo chicken breast samples pre- and post-hydration. Estimates of SWA were computed using the frequency-shift (FS) and the attenuation measuring shear wave elastography (AMUSE) methods. Dispersion slopes were computed from the phase velocity dispersion curves. The SWA coefficient estimates were strongly correlated with the fluid percentages in phantoms (r = 0.86 and 0.92 for FS and AMUSE methods, respectively, p < 0.001). However, no trends were observed for dispersion slope estimates (r = -0.73, p < 0.001). Thus, SWA was found to be a more sensitive parameter than the dispersion slope for differentiating phantoms with a range of in situ fluid content. Additionally, when phantoms were subjected to compression, SWA was sensitive to changes in compression-induced fluid variations in situ (p < 0.05), but dispersion slope showed no such trends (p = 0.12). The SWA estimates of ex vivo samples significantly increased post-hydration using both methods (p < 0.05), while the dispersion slope decreased. The findings of this study demonstrate that SWA is sensitive to fluid content in situ, which motivates its further development as a marker to assess pathological conditions.