Quantification of liver fat and fibrosis using elastography plus composite theory

Abstract

There are a growing set of ultrasound and viscoelastic measures that can be correlated with fat or fibrosis in the liver. We find that fat and fibrosis jointly influence important properties of the liver and can be considered as confounding cofactors within most simple measures. For example, shear wave attenuation is sensitive to the accumulation of viscous fat, but is also influenced by the degree of fibrosis, so attenuation by itself is insufficient for accurate estimation of liver fat. However, using some robust elastography techniques to assess both the shear wave phase velocity and the shear wave attenuation in a region of the liver, these measured values are found to be sufficient information for solving for both the unknown fat percent volume and the liver stiffness related to fibrosis score. A classical theory of composite viscoelastic materials is used to solve for the unknowns. Examples from human clinical studies are shown to correspond to biopsy proven grades of steatosis and fibrosis.