Dispersion analysis in skin using FEM: Characterizing the effects of the lower boundary material on the propagation of shear waves

Skin represents a complex structure for the quantification of viscoelastic (VE) properties using shear waves. Wave propagation through skin has been modeled as propagating both as a Lamb wave and as a Rayleigh wave, but both assumptions are limited due to the structure of the skin, which is a multi-layered tissue. This complexity of structure makes it difficult to accurately assess the relative contributions of geometry and viscosity to shear wave dispersion. In this study we used finite element modeling (FEM) to simulate the layering and VE properties of skin and subcutaneous tissues to assess characteristics of shear wave propagation through skin. Results were compared to the expected solutions using pure Rayleigh wave or Lamb wave models. From the simulation it was established that under most physiological circumstances the Lamb wave model is more appropriate than the Rayleigh wave model, higher frequencies should be used for viscoelasticity characterization, and imaging thicker regions of skin facilitates higher accuracy for characterizing its VE properties.