Scattering of polarized light by biological tissues

Polarized light can be used to obtain images of superficial tissue layers such as skin and some example images are presented. This paper presents a study of the transition of linearly polarized light into randomly polarized light during light propagation through tissues. The transition of polarization was studied in polystyrene microsphere solutions and in chicken muscle (breast) and liver. The transition is discussed in terms of a diffusion process characterized by an angular diffusivity [radians²/mean free path] for the change in angular orientation of linearly polarized light per unit optical path traveled by the light. The results are consistent with the hypothesis that birefringent tissues randomize linearly polarized light more rapidly than nonbirefringent tissues. The results suggest that polarized light imaging of skin yields images based only on photons backscattered from the superficial epidermal and initial papillary dermis because the birefringent dermal collagen rapidly randomizes polarized light. This anatomical region of the skin is where cancer commonly arises.