Mueller microscopy of anisotropic scattering media: theory and experiments

The combined approach including experiments (Mueller polarimetry) and theory (differential Mueller matrix formalism) for the studies of anisotropic scattering media was tested on the model system of human skin. Custom-build Mueller polarimetric microscope was used for the studies of histological cuts of full-thickness skin equivalents generated from epidermal keratinocytes forming a multilayered epidermis on top of collagen I hydrogel with dermal fibroblasts. The sets of fixed unstained tissue cuts of different thicknesses (5mm - 30mm) were measured in transmission configuration. The values of polarimetric (dichroism and retardance) and depolarization parameters were calculated by applying pixel-wise the logarithmic decomposition of Mueller matrices. The parabolic dependence of depolarization parameters and linear dependence of polarimetric parameters on thickness, as predicted by theory, was confirmed by measurements. It proves that phenomenological modeling of complex anisotropic scattering medium (e.g., biological tissue) may effectively disentangle the polarimetric and depolarizing properties of the system understudies and may be used for analysis and diagnostics of tissue.