Retardance and depolarization of brain white matter as markers for intraoperative delineation of brain tumors: experiments and simulations

An accurate distinction between brain tumors and tumorless brain tissue is crucial for effective surgical resection. Polarization-sensitive optical imaging exploits birefringence differences, offering contrast between the optically anisotropic white matter of the tumorless brain and the optically isotropic brain tumor tissue. However, crossing brain fiber bundles within tumorless brain tissue may also erase such optical anisotropy. We use a polarized Monte Carlo algorithm to model backscattered wide-field Mueller matrix images of the optical phantoms of the brain's white matter. We compare the impact of fiber bundle crossing and the presence of an optically isotropic subsurface tumor across varying depths to mimic brain tissue removal during neurosurgery. The simulation results demonstrate that the depolarization dependence on depth may serve as a decisive parameter to distinguish the tumor and fiber bundles crossing zones, as the values of linear retardance drop in both zones, whereas the depolarization values become smaller in the tumor zone.