Wideband optical elastography of in vivo human skin using geometrically focused surface waves

Viscoelastic models are fit to shear moduli derived from geometrically focused surface waves (GFS) on human skin using viscoelastic wave theory. Unlike in previous studies on the analytical solution and experimental measurement of radially outward traveling surface waves, measurable radially inward traveling GFS waves can be generated over a wider range of frequencies as attenuation is countered by the converging nature of the wavefront. This enables a more accurate and broader assessment of both the shear storage and loss moduli of the material, which are expected to vary with frequency. In the present study, GFS waves are applied to human skin on the posterior side of the forearm using a scanning LASER Doppler vibrometer. Surface wave measurements can then be used to estimate the complex frequency dependent viscoelastic properties of biological tissue, which are affected by numerous pathologies. Using a phantom gel this technique was validated through comparison with other studies. It was found that spring-pot and fractional Voigt models yield a potentially stable model parameter for skin, but more study is needed to confirm. [Work supported by NIH: Grant # EB012142.]