P4‐179: In vivo tau imaging in Alzheimer's disease and other dementias

26 6 3) and 23 cognitively normal controls (CN; 67 6 6 yrs) were enrolled. Full volume inversion recovery (TI 300, 1800, 3200, and no inversion pulse) MPRAGE datasets (1 mm 2 in-plane resolution) were acquired on a 7T Siemens scanner at baseline and 12, 30, and 44 min after CR (gadoteridol) injection (0.11mmol/kg). R 1 maps were prepared after image co-registration and voxelwise evaluation of the Bloch equation for each variable TI dataset accounting for all RF pulses and delays. IR-MPRAGE structural images were also acquired. A mask was applied to R 1 maps to define a region of interest in the lateral ventricles superior to the fornix and free from any visual choroid plexus. PVH severity was scored using the Fazekas rating scale. Results: CSF volume correlates inversely with baseline ventricular 1 H 2 O R 1 values (r1⁄4 -0.45), consistent with a lower macromolecular content with ventricular dilatation. The expected agerelated increase in CSF volume is also observed (r1⁄4 0.74). Ventricular 1 H 2 O R 1 values increase at each time point after CR injection (P1⁄4 0.04) and are significantly associated with PVH score (P1⁄4 0.003; repeated measures ANOVA). Group (AD v CN) effects are not significant. Conclusions: Administration of CR increases 1 H 2 O R 1 in the ventricles of the elderly brain. In the context of a relatively intact blood-brain barrier, the temporal changes in R 1 likely reflect leakage of CR across the BCSFB (ca. 2 mM hr -1). The increased rate of R 1 change after CR administration in the presence of PVHs suggests that PVHs and increased BCSFB permeability may share a common pathology.