Reflectance full Mueller matrix polarimetry for microstructural validation of diffusion magnetic resonance imaging

Knowledge of fiber microstructure and orientation in the brain is critical for understanding the pathogenesis and progression of neurodegenerative diseases such as Alzheimer's Disease. Diffusion magnetic resonance imaging (dMRI) is a noninvasive imaging modality that can generate mappings of nerve fiber orientation. Due to rigorous levels of mathematical modeling involved in reconstructing dMRI data; and limited spatial resolution, there arises a need to validate the biological accuracy of collected dMRI data. Polarized light imaging (PLI) has been shown to have potential for microstructural validation due to the anisotropy in many biological tissues, particularly in myelin sheaths surrounding nerve fibers in the brain. Using PLI for this purpose is appealing because it is directly sensitive to tissue structure and can be done at high resolution. While several studies have had success using PLI for fiber mapping, continuing to advance this modality, particularly reflectance based PLI systems, could provide a valuable avenue for in vivo neural imaging. In order to reach the full potential of reflectance PLI systems, some key questions remain such as the ability of PLI to resolve crossing fibers, and the sensitivity of reflectance PLI to fiber inclination. Tissue phantoms are one potential method to isolate these issues in order to investigate them. In this proceeding, a five-wavelength reflectance Mueller Matrix polarimeter is used for imaging of promising PLI tissue phantoms as well as regions of interest in fixed ferret brain samples. The retardance, diattenuation and depolarization mappings are derived from the Mueller matrix and studied in order to assess the sensitivity of this polarimeter configuration to different fiber orientations.