Hyperspectral measurement of the scattering of polarized light by skin

The goal of this study is to develop a spectropolarimeter for purposes of assessing polarization signatures in skin scattering on a regional scale. Prior research has that certain skin lesions have identifiable polarization signatures;1-3 however, those studies were limited to single lesion evaluation and are not convenient for screening patients with many suspicious legions. As a precursor to the future instrument, a simple actively illuminated Stokes spectropolarimeter was constructed to gather preliminary data about expected signatures and the required performance (resolution, wavelength, polarization state, etc.). This spectropolarimeter consists of a rotating retarder and a hyperspectral camera4 that scans through wavelengths by means of a Liquid Crystal Tunable Filter (LCTF). Data is captured in a serial fashion, where LCTF scans through eight wavelengths at each of the four retarder orientations. With a single acquisition taking 23 seconds to complete, it makes the issue of image registration very important. After proper alignment, the acquired images reveal that wavelength-dependent polarization signatures exist on a regional scale. In particular, it was found that polarization factors such as Degree of Linear Polarization (DoLP) tend to suppress many uninteresting skin features like wrinkles and skin texture, while capturing information that is not necessarily apparent in the intensity image.