In vivo optical reflectance imaging of spreading depression waves in rat brain with and without focal cerebral ischemia

Spreading depression (SD) waves occur in focal cerebral ischemia of the brain. Optical reflectance imaging at 550 +/- 10-nm wavelength using a charge-coupled device (CCD) camera, called optical intrinsic signal imaging (OISI) in the neuroscience community, provides high resolution imaging of SD waves based on changes in blood perfusion. We present optical images of SD waves in normal rat brain induced by a pinprick, and the spontaneous SD waves that follow middle cerebral artery occlusion (MCAO). The images of change in reflectance are calculated as A=(I-I-o)/I-o, where I is pixel intensity as some timepoint and I-o is the initial intensity just prior to an SD wave. Difference images B=[I(i)-I(i-1)]/I-o, where I(i) is the image at time i and I(i-1) is the previous image at time i-1 (a 6.4-s interval), significantly sharpen the boundaries between leading and trailing edges of the SD wave. Maximum rate-of-change images C=max(B) display the maximum pixel value of B within the duration of a single SD wave, and provide an image that visualizes the entire penumbra. The penumbra appear bright due to a rapid drop in perfusion, while the normal brain and infarct area appear dark. (c) 2006 Society of Photo-Optical Instrumentation Engineers.