Boundary conditions for light propagation in diffusive media with nonscattering regions

The diffusion approximation proves to be valid for light propagation in hig hly scattering media, but it breaks down in the presence of nonscattering r egions. We present a compact expression of the boundary conditions for diff usive media with nonscattering regions, taking into account small-index mis match. Results fi om an integral method based on the extinction theorem bou ndary condition are contrasted with both Monte Carlo and finite-element-met hod simulations, and a study of its limit of validity is presented. These p rocedures are illustrated by considering the case of the cerebro-spinal flu id in the brain, for which we demonstrate that for practical situations in light diffusion, these boundary conditions yield accurate results. (C) 2000 Optical Society of America [S0740-3232(00)00409-9] OCIS codes: 170.5270, 2 90.1990.