Abstract
The nerve fiber bundles constitutive of the white matter in the brain are organized in such a way that they exhibit a certain degree of structural anisotropy and birefringence. The birefringence exhibited by such aligned fibrous tissue is known to be extremely sensitive to small pathological alterations. Indeed, highly aligned anisotropic fibers exhibit higher birefringence than structures with weaker alignment and anisotropy, such as cancerous tissue. In this study, we performed experiments on thick coronal slices of a healthy human brain to explore the possibility of (i) measuring, with a polarimetric microscope the birefringence exhibited by the white matter and (ii) relating the measured birefringence to the fiber orientation and the degree of alignment. This is done by analyzing the spatial distribution of the degree of polarization of the backscattered light and its variation with the polarization state of the probing beam. We demonstrate that polarimetry can be used to reliably distinguish between white and gray matter, which might help to intraoperatively delineate unstructured tumorous tissue and well organized healthy brain tissue. In addition, we show that our technique is able to sensitively reconstruct the local mean nerve fiber orientation in the brain, which can help to guide tumor resections by identifying vital nerve fiber trajectories thereby improving the outcome of the brain surgery.
Highlights
Cancer is a global burden that leads to public health and economic problems and ranks as the first or second leading cause of premature death [1]
The key difference between gray and white matter of the brain is that gray matter majoritarily comprises of nucleon cells while white matter comprises of nerve fibers
We used polarimetric imaging to investigate the structural anisotropy of different regions in a coronal cross-section of a human brain
Summary
Cancer is a global burden that leads to public health and economic problems and ranks as the first or second leading cause of premature death [1]. The primary treatment for a brain tumor is surgery followed by adjuvant chemo or radio therapy. I.e., removal the bulk of cancer cells, is paramount for an improved prognosis. The accuracy of the estimation of the tumor’s borders carries heavy consequences for the patients: on one hand, subtotal resection leads to increased risk of recurrence and shorter life expectancy [4,5,6] and, on the other hand, if healthy tissue is removed as a result of gross resection, this might irrevocably damage the brain, leading to irreversible disabilities and a decreased quality of life which again might decrease life expectancy [7]. The accurate resection of the malignant tumor is a fundamental prerequisite for efficient adjuvant therapy [8,9]. The prime difficulty resides in identifying clear borders to the tumorous cells to define adequate safety margins given the infiltrative nature of most brain tumor types [10,11]
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