Polarization measurements give orthogonal information to spectral images making them a great tool in the
characterization of environmental parameters in nature. Thus, polarization imagery has proven to be remarkably useful
in a vast range of biomedical applications. One such application is the early diagnosis of flat cancerous lesions in murine
colorectal tumor models, where polarization data complements NIR fluorescence analysis. Advances in nanotechnology
have led to compact and precise bio-inspired imaging sensors capable of accurately co-registering multidimensional
spectral and polarization information. As more applications emerge for these imagers, the optics used in these
instruments get very complex and can potentially compromise the original polarization state of the incident light. Here
we present a complete optical and polarization characterization of three rigid endoscopes of size 1.9mm x 10cm (Karl
Storz, Germany), 5mm x 30cm, and 10mm x 33cm (Olympus, Germany), used in colonoscopy for the prevention of
colitis-associated cancer. Characterization results show that the telescope optics act as retarders and effectively
depolarize the linear component. These incorrect readings can cause false-positives or false-negatives leading to an
improper diagnosis. In this paper, we offer a polarization calibration scheme for these endoscopes based on Mueller
calculus. By modeling the optical properties from training data as real-valued Mueller matrices, we are able to
successfully reconstruct the initial polarization state acquired by the imaging system.
|