Search

Finite difference time domain (FDTD) analysis has been successfully formulated for solving diffusion equation in biological tissues. Time-dependent diffusion equations are approximated by FDTD equations by assigning diffuse photon fluence rates and radiant flux defined in the diffusion equations to Yee meshes. At the boundary between scattering and no scattering material, FDTD equation including only fluence rate has been derived, which make it possible to calculate the fluence rate at the boundary. The formulation is useful to solve diffusion equations by iterative algebraic calculations in scattering media with inhomogeneous optical properties. The conditions to give stabilities for numerical solutions have been become clear in terms of scattering coefficients and mean cosine of scattering angles. Using the formulation, the reflectance of three-layered slabs containing a clear layer have been calculated. As a result, it has been found that absorption loss changes of the highly scattering medium beyond the clear layer are estimated from the time profiles of the reflectance. Index Terms--Diffusion equation, FDTD analysis, optical computer tomography, transmittance and reflectance.

A study on the use of the seismic transmission traveltime tomography technique proposes a reconstruction method to improve on the conventional singular value decomposition approaches by combining suitable weighing matrices and a variable regularization parameter. Experimental results indicate that the proposed reconstruction approach can strike a good balance between resolution and stability for an ill-posed problem without focusing too closely on the issue of parameter selection.