In vivo optical microscopy of peripheral nerve myelination with polarization sensitive-optical coherence tomography.

Assessing nerve integrity and myelination after injury is necessary to provide insight for treatment strategies aimed at restoring neuromuscular function. Currently, this is largely done with electrical analysis, which lacks direct quantitative information. In vivo optical imaging with sufficient imaging depth and resolution could be used to assess the nerve microarchitecture. In this study, we examine the use of polarization sensitive-optical coherence tomography (PS-OCT) to quantitatively assess the sciatic nerve microenvironment through measurements of birefringence after applying a nerve crush injury in a rat model. Initial loss of function and subsequent recovery were demonstrated by calculating the sciatic function index (SFI). We found that the PS-OCT phase retardation slope, which is proportional to birefringence, increased monotonically with the SFI. Additionally, histomorphometric analysis of the myelin thickness and g-ratio shows that the PS-OCT slope is a good indicator of myelin health and recovery after injury. These results demonstrate that PS-OCT is capable of providing nondestructive and quantitative assessment of nerve health after injury and shows promise for continued use both clinically and experimentally in neuroscience.

Decreased light attenuation in cerebral cortex during cerebral edema detected using optical coherence tomography.

Cerebral edema develops in response to a variety of conditions, including traumatic brain injury and stroke, and contributes to the poor prognosis associated with these injuries. This study examines the use of optical coherence tomography (OCT) for detecting cerebral edema in vivo. Three-dimensional imaging of an in vivo water intoxication model in mice was performed using a spectral-domain OCT system centered at 1300 nm. The change in attenuation coefficient was calculated and cerebral blood flow was analyzed using Doppler OCT techniques. We found that the average attenuation coefficient in the cerebral cortex decreased over time as edema progressed. The initial decrease began within minutes of inducing cerebral edema and a maximum decrease of 8% was observed by the end of the experiment. Additionally, cerebral blood flow slowed during late-stage edema. Analysis of local regions revealed the same trend at various locations in the brain, consistent with the global nature of the cerebral edema model used in this study. These results demonstrate that OCT is capable of detecting in vivo optical changes occurring due to cerebral edema and highlights the potential of OCT for precise spatiotemporal detection of cerebral edema.