Generalized fokker-planck models of light propagation in layered media

We present a numerical procedure using the P_N-method to model light distributions in layered structures such as the epithelium. In contrast to previous studies of layered media using Monte Carlo methods and discrete ordinates, the P_N-method provides the flexibility to not only vary tissue optical properties across layers but also allows one to vary the tissue light interaction without changes to the numerical method. This includes the collection of generalized Fokker-Planck equations used in forward scattering approximations. Example calculations are performed for a model of the head consisting of a skull layer, cerebrospinal fluid layer, and cortex layer and a model of a port wine stain consisting of epidermis, dermis, and vascular malformation layers. Results obtained with the P_N-method are shown to agree with Monte Carlo simulation but are obtained in a fraction of the time needed for accurate Monte Carlo results.