Role of anisotropy in elastographic tissue characterization

Abstract

The structure and function of soft tissues are intimately connected. Some soft tissues are organized in such a way that they have material properties that are anisotropic, that is, the measured properties depend on which direction they are measured. Some such tissues are the brain, kidney, arteries, and cardiac and skeletal muscle. We will provide a brief overview of work targeted at characterization of the anisotropic mechanical properties in kidney and cardiac and skeletal muscles. In many cases, these tissues can be assumed to be transversely isotropic, which allows for simplification in estimating their mechanical properties. The use of propagating shear waves can be used to determine these mechanical properties. As a comparison example, we will show data from characterization of renal tissue with ultrasound shear wave elastography (SWE) and optical coherence elastography. We will also provide an overview of evaluation of skeletal muscle mechanical properties using shear wave elastography techniques and use of model fitting to estimate mechanical properties. Special care must be taken in evaluation of such anisotropic tissues to ensure that measurements are standardized across practices and studies.