In optical imaging, the high random scattering of light in biological tissue can degrade the contrast of an image which could be a drawback in detection of tumors. Polarization based imaging has shown its capability in overcoming such drawbacks over the recent years. It depends on discrimination of randomly polarized light from weakly polarized light yielding an enhanced image contrast. The purpose of this research study was to investigate, compare and assess the imaging potential of two widely used techniques in the field of polarimetric imaging namely, Linear Polarimeter method (uses linearly polarized light) and Rotating Retarder Polarimeter method (uses circularly polarized light) to interrogate targets embedded in turbid biological media. This novel study may contribute to early detection of diseases and pathologies in biological tissues.
The polarization properties of the backscattered light from a turbid medium containing a target submerged in a scattering solution were studied. A preclinical optical phantom was designed and the experiments were done in two phases, each phase corresponding to a different polarimetric technique. Specifically, a polystyrene cylinder was used as the target and the turbid medium was simulated by adding skim milk in volume percentage increments in both the phases. The first phase of experiments involved the Rotating Retarder Polarimeter method and the Polarimetric Measurement Matrix Reduction techniques. The images obtained by this method were processed by
means of a data reduction algorithm, based on Polarimetric Measurement matrix method to calculate the Degree of Linear Polarization (DOLP) image and total intensity (S0) image. The second phase of experiments involved the Linear Polarimeter method. The resulting co-polarized and cross-polarized images from this method were processed to obtain Degree of Polarization (Rpol) images. Both of these experiments were performed using a backscattered polarimetric imaging system.
The images obtained by both the techniques were analyzed by computing signal to background ratio (SBR) values and number of pixels detected as edges for every concentration of skim milk solution added to the surrounding medium of the target. The obtained images were then compared to determine the image quality.
Experimental results from both these techniques showed that the DOLP images obtained by the Rotating Retarder Polarimeter method provide better contrast in terms of signal to background ratio (SBR) values and number of pixels detected as edges compared to Degree of Polarization (Rpol) images obtained by the linear Polarimeter method. Overall, the contributions of this study suggest that the interrogation of targets in turbid media using circularly polarized light exhibits superior imaging characteristics with respect to linearly polarized light interrogation.