Time-Resolved Noninvasive Optical Parameters Determination in Three-Dimensional Biological Tissue Using Finite Difference Time Domain Analysis with Nonuniform Grids for Diffusion Equations

The finite difference time domain (FDTD) analysis based on nonuniform grids for solving the diffusion equations in biological tissue has been proposed. It has been confirmed that the analysis greatly reduce the time for calculating time-resolved reflectance in three-dimensional scattering medium preserving the numerical accuracies. Based on the analysis, noninvasive optical parameters determination in three-dimensional inhomogeneous medium divided into 192 homogeneous cubic cell 10 (mm) in edge lengths has been studied. Chi-square fitting for theoretical and experimental time-resolved reflectance was optimized by the downhill simplex method. As a result, it has been become clear that absorption coefficients in all cubic cells in scattering medium are estimated within the accuracy of 10% by utilizing only time-resolved reflectance