Polarized light imaging specifies the anisotropy of light scattering in the superficial layer of a tissue

This report describes how optical images acquired using linearly polarized light can specify the anisotropy of scattering (g) and the ratio of reduced scattering [μs′=μs(1-g)] to absorption (μa), i.e., N′=μs′/μa. A camera acquired copolarized (HH) and crosspolarized (HV) reflectance images of a tissue (skin), which yielded images based on the intensity (I=HH+HV) and difference (Q=HH-HV) of reflectance images. Monte Carlo simulations generated an analysis grid (or lookup table), which mapped Q and I into a grid of g versus N′, i.e., g(Q,I) and N′(Q,I). The anisotropy g is interesting because it is sensitive to the submicrometer structure of biological tissues. Hence, polarized light imaging can monitor shifts in the submicrometer (50 to 1000 nm) structure of tissues. The Q values for forearm skin on two subjects (one Caucasian, one pigmented) were in the range of 0.046±0.007 (24), which is the mean±SD for 24 measurements on 8 skin sites×3 visible wavelengths, 470, 524, and 625 nm, which indicated g values of 0.67±0.07 (24).