Hybrid Monte Carlo for photon transport through optically thick scatteringmedia

A Monte Carlo simulation code developed to model time-domain transilluminat ion measurements with small-area detectors through an optically thick scatt ering slab is presented. A hybrid approach has been implemented to reduce c alculation times. Most of the scattering slab is treated stochastically, al beit with variance reduction techniques and the isotropic diffusion similar ity rule. The contribution to the output signal per unit area and time of p hoton packets propagating in a thin slice near the output face of the slab is calculated analytically after each propagation step. This approach drast ically reduces the calculation time but produces spikes in the temporal sig nals. (C) 1999 Optical Society of America.