Tissue polarimetric study I: In search of reference parameters and depolarizing Mueller matrix model of ex vivo colon samples

Upon polarimetry the polarization state of light can be obtained for different depolarizing or non-depolarizing medias such as biological specimens. Tissue polarimetry can facilitate a differentiation between healthy and (pre)cancerous tissues, without using any contrast agents and ionizing radiation. Early cancer detection is vital to increase the life expectancy of patients. Turbid medias like biological tissues can change the state and/or decrease the initial polarization of light. Circularly polarized light is preferred as found to possess better ability to detect abnormal changes in tissues, compared to linearly polarized light. In this paper we analyse polarimetric parameters, measured with Thorlabs Stokes meter included in tissue polarimetric experimental set- up in reflection geometry and multiple ex vivo colon samples. The polarimetric device operates in the spectral range between 400 nm and 700 nm, where all experiments had been conducted with wavelength of 635 nm. By reaching reference values for the polarimetric parameters we can propose a theoretical Mueller matrix, that can be used to describe the depolarization properties of the colon samples used in the experiments. The proposed Mueller matrix is to be modelled and experimentally validated to find out if it matches the theory and can be further decomposed to three matrices of depolarization, diattenuation and retardance. All of the aforementioned experimental approaches are a step closer to a pre-clinical trial, which is a bridge to the final and the most challenging goal - tissue polarimetric set-up for in vivo diagnostics.