Experimental validation of a recently developed model for single-fiber reflectance spectroscopy

Significance: We recently developed a model for the reflectance measured with (multi-diameter) single-fiber reflectance (SFR) spectroscopy as a function of the reduced scattering coefficient μs0, the absorption coefficient μa, and the phase function parameter psb. We validated this model with simulations. Aim: We validate our model experimentally. To prevent overfitting, we investigate the wavelength-dependence of psb and propose a parametrization with only three parameters. We also investigate whether this parametrization enables measurements with a single fiber, as opposed to multiple fibers used in multi-diameter SFR (MDSFR). Approach: We validate our model on 16 phantoms with two concentrations of Intralipid-20% (μs0 ¼ 13 and 21 cm−1 at 500 nm) and eight concentrations of Evans Blue (μa ¼ 1 to 20 cm−1 at 605 nm). We parametrize psb as 10−5 · ðp1ðλ∕650Þ þ p2ðλ∕650Þ2 þ p3ðλ∕650Þ3Þ. Results: Average errors were 7% for μs0, 11% for μa, and 16% with the parametrization of psb; and 7%, 17%, and 16%, respectively, without. The parametrization of psb improved the fit speed 25 times (94 s to <4 s). Average errors for only one fiber were 50%, 33%, and 186%, respectively. Conclusions: Our recently developed model provides accurate results for MDSFR measurements but not for a single fiber. The psb parametrization prevents overfitting and speeds up the fit.