In this study, we present an empirically modified diffusion model determining hemoglobin oxygen saturation from turbid media using steady-state, broadband (500-600 nm) reflectance with source-detector separations of a few hundred micrometers. Development of this model was conducted using Monte Carlo simulations, a gold standard modeling technique for predicting the behavior of light propagation through turbid media. Hemoglobin oxygen saturation levels of 0 and 100% at different blood concentrations were studied. Nonlinear curve fitting was used to extract the hemoglobin oxygen saturation values from the reflectance spectra, producing errors of 5% between the simulated curves and the model for both saturation cases. Further validation was performed using liquid-tissue phantoms containing intralipid and blood. Curve fitting between the in vitro data and the model produced errors of less than 2%. This validated model was then used to extract saturation values from in vivo reflectance spectra of the human index finger and human brain tissues. This empirically modified diffusion model provides the possibility of extracting local hemoglobin oxygen saturation from blood-perfused turbid media using reflectance data measured with a small source-detector separation probe.
Maureen Johns, Cole A. Giller, and Hanli Liu, "Determination of Hemoglobin Oxygen Saturation from Turbid Media Using Reflectance Spectroscopy with Small Source-Detector Separations," Appl. Spectrosc. 55, 1686-1694 (2001)