Localization of nerve fiber bundles by polarization-sensitive optical coherence tomography

Diagnostic modalities that can distinguish brain tumors from eloquent cortices or nerve fiber bundles are important for neurosurgery. For identifying nerve fiber bundles, various techniques such as diffusion tensor imaging and subcortical stimulation mapping have been used. In this article, we propose localization of nerve fiber bundles by polarization-sensitive optical coherence tomography (PS-OCT) for the first time. PS-OCT performs tomographic imaging by measuring the travel distance and the change in polarization of the backscattered light from the tissue at different traverse positions, enabling selective visualization of birefringent tissues such as nerve fiber bundles. We examined the imaging of nerve fiber bundles in blocks of fixed rat brains. Nerve fiber bundles in internal and external capsules of the rat brains appearing on the surfaces of the coronal, horizontal, and sagittal planes were identified as to their locations and orientations. The nerve fiber bundles were clearly visualized by PS-OCT. The image penetration depth of the PS-OCT images was about 1.0 mm in gray matter and about 0.5 mm in white matter, so the refractive indices of gray and white matters were assumed to be 1.4.