Neurophotonics refers to the scientific field that studies the interaction of light with neural tissue. This is a rapidly growing field with great potential for the development of optical diagnostic devices for a number of brain conditions.

In particular, our laboratory has focused on developing optical methods to (i) detect seizure activity; and (ii) to detect brain swelling (cerebral edema). Based on previous findings from the laboratory that indicated that there is constriction of extracellular space prior to seizure onset, Binder reasoned that the mechanism for this is likely pre-seizure astrocyte swelling and that this should be optically detectable. Indeed, we have found that there is a reduction in near-infrared (NIR) reflectance preceding seizure onset.

Figure 1. Brain surface exposed for imaging.

In separate work, we are in the process of developing methods for optical detection of brain swelling. Cerebral edema (brain swelling), an increase in brain water content, is responsible for significant morbidity and mortality in many neurological diseases, including traumatic brain injury (TBI), stroke, infection, and brain tumors. For example, following TBI, affected individuals experience delayed onset of cerebral edema which can lead to raised intracranial pressure (ICP), brain herniation, and death. Acute neurological emergencies like TBI including gunshot wounds to the head (as recently publicized with the shooting of U.S. Representative Gabrielle Giffords) require point-of-care advanced neuromonitoring devices to directly provide important real-time information about the brain to clinicians to enable them to act quickly and decisively to ensure the best outcome. It is clear that significant secondary injury to the brain would be avoided if cerebral edema could be detected early.

Figure 2. Brain cortex extracellular space stained with green fluorescent marker in vivo.

We have developed a method of detecting cerebral edema directly through the use of optics. In particular, we have discovered that the scattering of near-infrared (NIR) light is a sensitive and direct indicator of early cerebral edema. We are now expanding on our early findings to develop a usable device for clinical application. To achieve maximum temporal and spatial resolution, we are adapting optical coherence tomography (OCT), an “optical ultrasound” imaging modality, to brain neurodiagnostic evaluation for the first time.

Figure 3. Example of in vivo brain optical coherence tomography (OCT) image. Depth profiles from regions of interest can be obtained and followed in real time for changes.