Unified analysis of the sensitivities of reflectance and path length to scattering variations in a diffusive medium.

A unified analysis is presented for the sensitivities of reflectance and path length to scattering variations in a diffusive medium, using an improved solution of the steady-state diffusion equation. This approach enables one to (1) explain theoretically two kinds of dependency of near-infrared reflectance on source-detector separations and (2) obtain an analytical expression for optical path lengths. The results shown here are consistent with those of Kumar and Schmitt [Appl. Opt. 36, 2286 (1997)] and Mourant et al. [Appl. Opt. 36, 5655 (1997)]. Also, discussions are given on (1) possible reasons for some inconsistency between the conclusion drawn by Mourant et al. and results given here and (2) the usefulness of making reflectance measurements while minimizing the sensitivity of reflectance and path length to scattering variations.