Determining light absorption changes in multilayered turbid media through analytically computed photon mean partial pathlengths

In this work we introduce a model for analytically computing the mean partial pathlengths (MPPLs) of photons in optically turbid media consisting in an arbitrary number of layers, being the deepest one infinitely thick. This has several applications in the field of Biomedical Optics, especially when modelling light propagation in biological tissues and systems such as the human head. The computational implementation of our model surpasses the current state-of-the-art calculations done by means of Monte Carlo (MC) simulations, which, despite their robustness, represent a bottleneck in terms of computation times and hardware requirements when real-time applications are considered. In order to validate the approach presented in this work, we compared it with MPPLs generated by MC simulations for turbid layered media with different numbers of layers and several combinations of optical properties and thicknesses. Results show a very good agreement between theory and simulations, with relative errors of less than 10% having place mainly in the first layer. It is expected that this investigation contributes to increasing the accuracy of the models currently used for studying light propagation in highly heterogeneous biological tissues.