Perturbation Monte Carlo methods to solve inverse photon migration problems in heterogeneous tissues

We introduce a novel and efficient method to provide solutions to inverse p hoton migration problems in heterogeneous turbid media. The method extracts derivative information from a single Monte Carlo simulation to permit the rapid determination of rates of change in the detected photon signal with r espect to perturbations in background tissue optical properties. We then fe ed this derivative information to a nonlinear optimization algorithm to det ermine the optical properties of the tissue heterogeneity under examination . We demonstrate the use of this approach to solve rapidly a two-region inv erse problem of photon migration in the transport regime, for which diffusi on-approximation-based approaches are not applicable. (C) 2001 Optical Soci ety of America.