Determination of chromophore concentrations from spatially resolved skin measurements

Chromophore concentrations from skin contain information about the blood parameters, for example total hemoglobin content or antioxidant status of the skin. Deviations from the normal values of the concentrations may indicate pathologies. As the chromophore concentrations are determined from skin absorption coefficients, the optical absorption spectra of the isolated skin chromophores have to be known in advance, enabling least squares fitting of the basis spectra to the skin absorption coefficient. It could be shown that spectrally and spatially resolved reflectance in combination with a determination of absorption and reduced scattering coefficients from a look-up table provides a means for quantification of chromophores, although the accuracy largely depends on the tissue model. Good qualitative results can also be obtained with the homogenous tissue model used here. For example, it could be shown that the hemoglobin basis spectra determined from human whole blood and the pure water absorption fit very well to the skin absorption coefficients, but the ex vivo carotene spectra does not. Therefore it was examined how the carotene spectra change from ex vivo to in vivo. Interindividual and interpositional variation of the optical parameters could also be evaluated using this method as well as the dependence of determined optical parameters on the source-detector separation.