Time-Resolved Reflectance from An Adult Head Model with Nonscattering Regions by The Finite-Difference Time-Domain Analysis Using New Boundary Conditions

Abstract

Time-resolved reflectance from an adult head model composed of multilayered slab with nonscattering regions has been predicted by the finite difference time domain analysis using new boundary conditions at the surface of scattering region. Light propagation across the nonscattering layer was calculated based on the light intensity characteristics along a ray in free space. Additional equivalent source functions due to light from scattering regions across the nonscattering region were introduced into the diffusion equation and an additional set of the diffusion equation was solved by FDTD analysis by employing new boundary conditions. The formulation was used to calculate time-resolved reflectances of four-layered slabs containing a nonscattering layer. The received light intensity and the mean time of flight estimated from the time-resolved reflectance are in reasonable agreement with previously reported experimental data and Monte Carlo simulations. The FDTD analysis was applied to estimate sensitivities in reflectance due to local absorption coefficient changes in gray matter in the model. It has been become clear that sensitivities are greatly enhanced in time-resolved reflectance and the source detector separations maximizing the sensitivities are strongly dependent on the existence of the nonscattering layer.