Influence of the high-order parameters on tissue spatially resolved reflectance

Influences of the second-order and third-order parameters of biological tissue on the spatially resolved diffuse reflectance are studied with Monte Carlo simulation. The reflectance R(ρ) is dependent on high-order moments of the tissues for a short source-detector separation, so the diffusion approximation theory fails to describe accurately R(ρ). It is found that the effective region of second-order parameter γ is about 5l_t, (transport mean free path), and the curve of the reflectance R(ρ) rises with γ in the region of 0.6l_t <ρ<5l_t.The effects of third-order parameter δ on the reflectance R(ρ) are studied, and the effective region is about 2l_t. We find that the curves of the reflectance R(ρ) depresses with δ in the region of 0.3l_t<p<2l_t, and the effect of γ on R_MC(ρ) appears irregular because that the effect of γ be counteracted by the effect of δ when the condition of Δδ≪Δγ is not satisfied.