Patlak plots of Gd-DTPA MRI data yield blood-brain transfer constants concordant with those of 14C-sucrose in areas of blood-brain opening

The blood-to-brain transfer rate constant (K-i) of Gd-DTPA was determined in MRI studies of a rat model of transient cerebral ischemia. The longitudinal relaxation rate, R-1, was estimated using repeated Look-Locker measurements. A model-independent analysis of DeltaR(1), the Patlak plot, produced maps of K-i for Gd-DTPA and the distribution volume of the mobile protons (V-p) with intravascular-Gd changed R-1's. The K-i'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 C-14-sucrose determined shortly thereafter by quantitative autoradiography. The K-i'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 r(2) = 0.72 (P = 0.01). Thus, K-i for Gd-DTPA varied in parallel with, but was less than, K-i for sucrose. In the ROIs, mean V-p 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 V-p in contralateral brain (0.015 ml g(-1)). This elevated V-p may reflect increased capillary permeability to water. In conclusion, K-i can be reliably calculated from Gd-DTPA-MRI data by Patlak plots. (C) 2003 Wiley-Liss, Inc.