Temporal correlation analysis of penumbral dynamics in focal cerebral ischemia. 
A novel temporal correlation technique was used to map the first-pass transit of iodinated contrast agents through the brain.  Transit profiles after bolus injections were measured with dynamic computed tomography (CT) scanning (1 image/s over 50 s).  A rabbit model of focal cerebral ischemia (n = 6) was used, and dynamic CT scans were performed at 30, 60, 90, and 120 min postocclusion.  Within the ischemic core, no bolus transit was detectable, demonstrating that complete ischemia was present after arterial occlusion.  In the periphery of the ischemic distribution, transit dynamics showed smaller peaks, broadened profiles, and overall delay in bolus transit.  A cross-correlation method was used to generate maps of delays in ischemic transit profiles compared with normal transit profiles from the contralateral hemisphere.  These maps showed that penumbral regions surrounding the ischemic core had significantly delayed bolus transit profiles.  Enlargement of the ischemic core over time (from 30 to 120 min postocclusion) was primarily accomplished by the progressive deterioration of the penumbral regions.  These results suggest that (a) temporal correlation methods can define regions of abnormal perfusion in focal cerebral ischemia, (b) peripheral regions of focal cerebral ischemia are characterized by delays in bolus transit profiles, and (c) these regions of bolus transit delay deteriorate over time and thus represent a hemodynamic penumbra.