Sensitivity analysis to optical properties of biological tissues subjected to a short-pulsed laser using the time-dependent radiative transfer equation

Abstract

Visible and near-infrared spectral range of light can be used for estimating the optical properties of a biological tissue in a non-invasive way starting from its response to an external light stimulus. A forward model based on the time-dependent radiative transfer equation, that accurately describes light propagation through such media, is considered and solved with a finite-volume method for the discretization of the spatial domain. Results in terms of fluence and of reflectance at the illuminated transparent or semi-transparent wall for liver and skin tissues subjected to a collimated short-pulsed near-infrared laser are presented and discussed. A sensitivity analysis of the reflectance in the time domain to the four optical parameters of the model shows that only two of them can be estimated: the asymmetry factor of the Henyey–Greenstein phase function as well as either the refractive index or the scattering coefficient of the tissue. The reduced model can be used to invert the experimental reflectance measured assuming the signal over noise ratio of the detector known in the corresponding non-invasive detection technique.