VISCO-ELASTIC MODELS FOR SOFT TISSUES

The simplest, and much utilized (despite its numerous shortcomings), model for soft tissue is based on the assumption of a linear elastic medium, although there is substantial evidence to suggest that soft tissue is, in fact, visco-elastic in nature. Here we discuss the simple and direct inclusion of visco-elastic concepts into descriptions of soft tissue. The two most elementary linear viscoelastic mechanical models (Maxwell and Kelvin-Voigt) are discussed. The wave equations for pressure propagation in these media are derived and their absorption and velocity dispersion characteristics are examined. One interesting feature is that explicit pulsed wave solutions may be derived in some cases. Another finding is that absorptive behavior may be characterized in a relative efficient manner, without recourse to the usual frequency-dependent description. The extent to which these media can be regarded as suitable for tissue modeling purposes is investigated. The incorporation of scattering into these models may be effected in the usual manner, except that scattering by absorption fluctuations is also predicted.