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The objectives are to measure the early time-course of the flows of blood, red cells, and plasma in brain tissue destined to infarct following arterial occlusion. The flux of fluorescent red blood cells (fRBCs) through venules and the arteriovenous transit times (AVTT) of fluorescein-labeled plasma albumin were periodically monitored in anesthetized adult Wistar rats before and up to 60 min after permanent ligations of several small branches of the middle cerebral artery. Of note, fRBC is a function of venular erythrocyte flow and volume, whereas AVTT is a function of plasma flow and volume in visible arteriole–capillary–venule units. In another group of anesthetized rats, local cerebral blood flow (lCBF) was measured 1 h after permanent arterial occlusion by [14C]iodoantipyrine (IAP) autoradiography. With this model of focal ischemia, the lesion is highly reproducible and involves part of the whisker barrel cortex. Infarction of this area was observed in 12 of 13 rats. From 10 to 60 min after arterial occlusion, AVTT was nearly four times longer in the ischemic barrel cortex than at the same site before ligations, and fRBC flux was 25%. Neither parameter changed appreciably over this time. After 60 min of ischemia, lCBF on the ipsilateral barrel cortex was 18% of that on the contralateral side and 15% of the sham control value for the same area of the barrel cortex. Since whole blood flow in the ischemic barrel cortex was

The blood-to-brain transfer rate constant (Ki) of Gd-DTPA was determined in MRI studies of a rat model of transient cerebral ischemia. The longitudinal relaxation rate, R1, was estimated using repeated Look-Locker measurements. A model-independent analysis of ΔR1, the Patlak plot, produced maps of Ki for Gd-DTPA and the distribution volume of the mobile protons (Vp) with intravascular-Gd changed R1's. The Ki's of Gd-DTPA were estimated in regions of interest with blood–brain barrier (BBB) opening (regions of interest, ROIs) and compared to those of 14C-sucrose determined shortly thereafter by quantitative autoradiography. The Ki's for both Gd-DTPA and sucrose were much higher than normal within the ROIs (n = 7); linear regression of Ki for Gd-DTPA vs. Ki for sucrose yielded a slope of 0.43 ± 0.11 and r2 = 0.72 (P = 0.01). Thus, Ki for Gd-DTPA varied in parallel with, but was less than, Ki for sucrose. In the ROIs, mean Vp was 0.071 ml g−1 and much higher than mean vascular volume estimated by dynamic-contrast-enhancement (0.013 ml g−1) or mean Vp in contralateral brain (0.015 ml g−1). This elevated Vp may reflect increased capillary permeability to water. In conclusion, Ki can be reliably calculated from Gd-DTPA-MRI data by Patlak plots. Magn Reson Med 50:283–292, 2003. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]