PVOH and spontaneous Raman-based images of spinal cord in the immediate aftermath of localized contusive injury obtained noninvasively and in vivo in a rat model using remitted light from a single spatially scanned laser

Abstract

We produce 2 kinds of images of spinal cord in the immediate aftermath of a localized contusive injury, noninvasively and in vivo in a rat model using remitted light from a single spatially scanned 830 nm laser. Two different processing algorithms/modalities were employed 1) the PVOH algorithm producing images based on the turbidity of the spinal cord tissue which includes the cerebrospinal fluid (CSF) and 2) Raman spectroscopy which allows images based on pH. Whereas PVOH requires relatively little data processing e.g., no separation of Raman and fluorescence emission for implementation, quantitative use of spontaneous Raman spectra to calculate e.g., pH requires careful separation and accounting for the presence of underlying fluorescence. We utilize an unbiased procedure i.e., no assumptions are made, that an unsupervised machine can execute based on the inherent differences in line widths for pure vibrational and vibronic transitions in fluid media, and the overall effect of heterogenous spectral broadening at physiological temperature. The fundamentally stronger signal to noise ratio for PVOH imaging allows much greater spatial resolution for the same collection times needed to construct the Raman based pH images. This proof of principle study is consistent with a hypothesis that fast localized change in the CSF pH, induced by the mechanical disruption of tissues during the injury, disrupts the delicate balance of chemical factors stabilizing the CSF phase stability. We suggest that this combination of new methodologies for real-time imaging of chemical and physical changes in spinal cords and other tissues could have many uses.