Influence of the phase function in generalized diffuse reflectance models: review of current formalisms and novel observations.

Diffuse reflectance spectroscopy, which has been demonstrated as a noninvasive diagnostic technique, relies on quantitative models for extracting optical property values from turbid media, such as biological tissues. We review and compare reflectance models that have been published, and we test similar models over a much wider range of measurement parameters than previously published, with specific focus on the effects of the scattering phase function and the source-detector distance. It has previously been shown that the dependence of a forward reflectance model on the scattering phase function can be described more accurately using a variable, γ, which is a more predictive variable for reflectance than the traditional anisotropy factor, g. We show that variations in the reflectance model due to the phase function are strongly dependent on the source-detector separation, and we identify a dimensionless scattering distance at which reflectance is insensitive to the phase function. Further, we evaluate how variations in the phase function and source-detector separation affect the accuracy of inverse property extraction. By simultaneously fitting two or more reflectance spectra, measured at different source-detector separations, we also demonstrate that an estimate of γ can be extracted, in addition to the reduced scattering and absorption coefficients.