Currently, there are two backscattering polarimetry schemes, namely the collinear reflection mode with normal incidence, and the non-collinear reflection one with obliquely incident illumination. To eliminate the surface reflection from the sample cost-effectively, the non-collinear backscattering Mueller matrix (MM) imaging setup always has an oblique incidence. Meanwhile, the uneven tissue surfaces can induce various relative oblique incidences inevitably, which can affect the polarimetry in a complicated manner. In this study, we systematically measured the MMs of experimental phantom and ex-vivo tissues under different oblique incident illuminations. Moreover, a Monte Carlo simulation program based on cylindrical scattering model was also adopted for further analysis and validation. Oblique incidence can induce various aberration on non, two and four periodic MM elements, leading to false-positive and false-negative information for tissue polarimetry. The findings presented in this study give the suggestions for appropriate incident angle selection in in vivo tissue polarimetric practices and can also be useful as valuable references for studying how to minimize the influence furtherly.
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