Analyzing the influence from oblique incidence on quantitively backscattering Mueller matrix polarimetry: a pilot ex-vivo tissue study

Abstract

Backscattering polarimetry can detect substantial microstructure information of media label-freely. Among the available polarimetric techniques, the backscattering Mueller matrix polarimetry provides a promising non-contact and quantitative tool for in-vivo tissue detection and clinical diagnosis. To eliminate the surface reflection from the sample cost-effectively, the non-collinear backscattering Mueller matrix imaging setup always has an oblique incidence. Meanwhile, for practical organ cavities imaged using polarimetric gastrointestinal endoscopy, the uneven tissue surfaces can induce various relative oblique incidences inevitably, which can affect the polarimetry in a complicated manner and needs to be considered for detailed study. Therefore, it is a critical issue to figure out the influence from oblique incidence on backscattering tissue polarimetry. To systematically analyze such the influence, we measured the Mueller matrices of experimental phantom and ex-vivo tissues with different incident angles, adopted a Monte Carlo simulation program based on cylindrical scattering model for further verification and analysis. Meanwhile, the results were quantitively evaluated using the Fourier transform, basic statistics and frequency distribution histograms. Both the experimental and simulated results demonstrate that, oblique incidence can induce different variations on non-periodic, two-periodic and four-periodic Mueller matrix elements, leading to false-positive and false-negative polarization information for tissue polarimetry. Moreover, a prominent oblique incidence can bring more dramatic signal variations such as phase drift and element transposition. The findings presented in this study give some crucial criterions of appropriate incident angle selections for in-vivo polarimetric endoscopy and other applications, and can also be valuable references for studying how to minimize the influence furtherly.