Modified diffusion models for steady-state broadband reflectance with a needle-like optic probe

Theoretical models available for optical reflectance with small source-detector separations are limited. In this study we reported two modified diffusion models for steady-state, broadband (500-590 nm) reflectance with source-detector separations of 0.125-0.25 mm and 0.25-1.0 mm. For the former case, the major modifications are D = 1/3μ_s' and z₀ = 1/μ_s'; for the latter case, an additional modification is to multiply the separation by a factor of 2. Monte Carlo simulations were used to confirm the modified models at three different hemoglobin concentrations with relative errors of 12% or smaller. These models provide the possibility to extract local optical and physiological parameters of blood-perfused tissues from reflectance data measured with a needle-like probe.