Previously, water exchange across the blood-brain barrier (BBB) and blood-cerebrospinal barrier (BCSFB) was assessed by multi-delay, multi-echotime (TE) arterial spin labeling, albeit in separate acquisitions with different settings. In this study, we present a protocol for simultaneous measurement of BBB and BCSFB water exchange using a multi-TE 3D-GRASE acquisition combined with T2-preparation. We evaluate several modeling approaches, comparing two- and three-compartment models to estimate water exchange rates from blood to gray matter (Kbl → GM), and to CSF (Kbl → CSF). ASL signal was consistent with expectations: at early time points, signal decayed rapidly across TEs in blood and GM, whereas at later time points decay was slower, consistent with label accumulation in CSF. All models yielded CBF and ATT values consistent with literature. Kbl → CSF was highest in the choroid plexus (≈1.75 × 10-2 s-1), with lower values in GM and subarachnoid space (≈1.4 × 10-2 s-1), and white matter (≈1.2 × 10-2 s-1) ROIs. In contrast, Kbl → GM was homogenous across the brain. The three-compartment model yielded similar Akaike Information Criterion values to the two-compartment model, but allows more insight into physiology and is thus preferred. Overall, the protocol allowed simultaneous characterization of BBB and BCSFB dynamics, with the three-compartment model offering the most informative representation of water exchange.
Petitclerc et al. (Tue,) studied this question.