ABSTRACT
Optical imaging (OI) has recently been introduced as an intraoperative technique for the localization of epileptic foci and eloquent cortex (1). OI detects variations in the scattering of incident light directed at the brain surface (2). These light-scattering variations, referred to as the intrinsic optical signal, are generated by multiple physiological processes associated with neuronal activity, including changes in blood oxygenation, blood volume, and extracellular volume (2). Current techniques such as electrocorticography (ECoG), electrical stimulation mapping (ESM), and functional imaging are limited in desired spatial and/or temporal resolution. With OI, however, it is possible to visualize epileptiform and functional activity over a broad range of spatial resolution from microscopic neuronal populations to macroscopic cortical regions with a temporal resolution of 200 msec. These benefits allow for greater accuracy in intraoperatively delineating Rolandic and language cortex, identifying interictal epileptiform discharges, pinpointing the onset of ictal events with precise localization, and directly observing the pathways by which seizure activity spreads. Because OI relies on physiological cortical activation rather than stimulation from external electrical currents, it can facilitate and enhance the intraoperative identification of cortical regions subserving cognitive functions. Though there are reports of OI in humans, it remains a research tool and will require further reliability testing and technical modifications before it can become feasible for routine clinical use.
