Patlak plots of Gd‐DTPA MRI data yield blood–brain transfer constants concordant with those of 14 C‐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 ΔR 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 14 C‐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 K i for Gd‐DTPA vs. K i 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. Magn Reson Med 50:283–292, 2003. © 2003 Wiley‐Liss, Inc.