The linearly polarized light incident to the tissue gives us different response from the surface and the bulk in the highly scattering tissues such as dermis, retina, etc.
The reflected light from the surface keeps the same polarization while the light reflected back from the layers in depth undergoes the multiple scattering that certainly depolarize the incident light. The de-polariztion ratio may account for the discrimination of the unhealthy from healthy tissues leading to the diagnosis of the disease.
The phenomena may contribute to diagnosis the diabetic retinopathy , dermal disorders and cutaneous and subcutaneous diseases.
We may model skin tissue as (melanin+oxyhomoglobin).
Melanin and hemoglobin absorption spectra:
Nishidate et. al has reported a multi-spectral diffuse reflectance imaging method based on a single snap shot of Red-Green-Blue images for estimating melanin concentration, blood concentration, and oxygen saturation in human skin tissue. Multiple regression analysis of the absorbance spectrum and the extinction coefficients of melanin, oxygenated hemoglobin and deoxygenated hemoglobin provides concentrations of melanin and total blood;
Sensors 2013, 13(6), 7902-7915; doi:10.3390/s130607902
R lies in the theraupatic window( 600-1200 nm) with low absorption and long penetration depth so gives more information from layers beneath + reflection from the surface.. B is far from this window having short penetration depth giving data mostly from the surface. Subtraction data due to R from B results in better resolution in depth.
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