Statistical basis for the determination of optical pathlength in tissue.

In this paper we show how to derive the mean and variance of the transilluminated signal obtained in models of light propagation in tissue, based both on a stochastic Monte Carlo method and on a deterministic diffusion approximation. The theoretical treatment of the Monte Carlo model applies only to integrated intensity measurements, whereas the diffusion approximation gives an estimator for the time-dependent case as well. We present results that show the accurate prediction of Monte Carlo statistics, and propose that the diffusion approximation is therefore a suitable mechanism for incorporating noise into modelling procedures.