A diffusion theory model of spatially resolved fluorescence from depth-dependent fluorophore concentrations

A photon diffusion model has been developed to calculate the steady-state s patially resolved fluorescence from pencil beam excitation in layered tissu e. The model allows the calculation of both the excitation reflectance and the fluorescence escape for an arbitrary continuous depth distribution of t issue optical properties and fluorophore concentration. The validity of thi s model was verified by comparison with Monte Carlo simulations and experim ental measurements using phantoms with tissue-like optical properties. The potential usefulness of the spatially resolved fluorescence was explored us ing the model and simulations of realistic drug distributions. It was shown that using this technique it may be possible to quantify the diffusion of a topically administered drug into the skin, or the photobleaching of a sen sitizer during photodynamic therapy.