The finite element model for the propagation of light in scattering media:A direct method for domains with nonscattering regions

We present a method for handling nonscattering regions within diffusing dom ains. The method develops from an iterative radiosity-diffusion approach us ing Green's functions that was computationally slow. Here we present an imp roved implementation using a finite element method (FEM) that is direct. Th e fundamental idea is to introduce extra equations into the standard diffus ion FEM to represent nondiffusive light propagation across a nonscattering region. By appropriate mesh node ordering the computational time is not muc h greater than for diffusion alone. We compare results from this method wit h those from a discrete ordinate transport code? and with Monte Carlo calcu lations. The agreement is very good, and, in addition, our scheme allows us to easily model time-dependent and frequency domain problems. (C) 2000 Ame rican Association of Physicists in Medicine. [S0094-2405(00)00901-9].