Generalized diffusion approximation for highly absorbing media and small source-detector separations

摘要

The diffusion approximation to the transport equation is commonly used in biomedical optical diagnostic techniques, but constrains its applicability to highly scattering system. The generalized diffusion approximation was developed by Venugopalan can be used to quantify optical properties of turbid media using small source detector separations and allow the measurement of media with highly absorption. Unfortunately, the simulated result from this theory was larger than the real value because δ -Eddington phase function contained too much forward scattering. Here a new independent control parameter is introduced to δ -Eddington phase function so as to modify the generalized diffusion approximation presented. The solution is presented in the stationary case for infinite media with a collimated source of finite size exhibiting spherical symmetry. The solution is compared to results given by the conventional diffusion theory, the generalized diffusion approximation as well as to the Monte-Carlo simulation in steady state diffusion equation for slab boundary condition. The simulation results show that the modified generalized diffusion approximation with an appropriate control parameter is more closed to Monte-Carlo simulation. The modified generalized formulation of diffusion theory presented here may enable the quantitative application of present optical diagnostic techniques to turbid systems which are more highly absorbing and allow these systems to be probed using smaller source-detector separations.