Shear wave dispersion for fibrosis, steatosis and activity staging

Quantitative elastography has been established as an efficient tool for chronic liver diseases non invasive diagnosis and staging. By estimating the velocity of shear waves propagating in the liver, the local shear modulus can be estimated, and, since it is correlated to the fibrosis level, can thus be used for non invasive fibrosis staging. But shear wave propagation also yields information on the viscosity and other medium properties than can be assessed under the assumption of a rheological model and could be interesting for diagnosis. In this study, Shear Wave Spectroscopy is compared with fibrosis, steatosis and activity assessed by liver biopsies. Results show that dispersion curves can be used for the determination of the fibrosis stage with good accuracy when parameters are physically linked to the medium stiffness. Shear Viscosity is also found to be linked to the fibrosis level which could be a consequence of the relationship between viscosity and shear modulus assumed by the Voigt Model. While the activity level can also be retrieved from those parameters, it is believed that the activity level is a direct consequence of the fibrosis level for most patients and not an independent indicator. Contrary to preliminary reports and hopes on the issue, steatosis is not found to be correlated to any of the parameters tested here.