Reliability of TRUST ASL for measuring cerebral blood flow and blood–brain barrier water exchange: a scan–rescan pilot study in healthy subjects and patients with epilepsy

Objective: Water exchange across the blood-brain barrier (BBB) sustains tissue homeostasis; BBB dysfunction can raise neuronal excitability and promote seizures. Noninvasive imaging of water exchange probes BBB function. T2l1lrelaxation underl1lspinl1ltagging (TRUST) arterial spin labeling (ASL) separates intravascular and extravascular labeled water. We tested TRUSTl1lASL feasibility and scan-rescan reliability. Methods: Twelve participants (5 controls, 7 with epilepsy) underwent two 3T MRI sessions 2-4 weeks apart, acquiring T1, FLAIR, and TRUSTl1lASL. At each epilepsy visit we recorded seizure frequency, last seizure details, and medications. ASL images were processed in MATLAB to quantify CBF and water exchange time. Maps were registered to T1 and normalized to MNI space via FreeSurfer. Scan-rescan reliability across gray matter and regions (temporal cortex including amygdala/hippocampus, frontal, occipitoparietal, basal ganglia) used intraclass correlation coefficients. Individual agreement was evaluated with Bland-Altman plots and withinl1lsubject coefficient of variation. Statistical analyses used R. Results: Scan-rescan reliability was good for CBF (ICC = 0.79, 95% CI 0.28 - 0.94) and excellent for water exchange time (ICC = 0.97, 95%CI 0.90-0.99) across grey matter. Regional analyses revealed lower reliability in the basal ganglia compared to other subregions. Bland-Altman analysis demonstrated strong agreement between sessions, with mean differences near zero for CBF (limits of agreement: -20 to 20 ml/100g/min), and water exchange time (mean differences 0.17s; limits of agreement: -0.44 to 0.79 s). Significance: Our findings show TRUSTl1lASL reliably measures BBB water exchange. Tex has high relative reliability (ICC) but substantial withinl1lsubject variability (wCV), limiting sensitivity for small individual longitudinal changes. Groupl1llevel reliability is strong, supporting use in longitudinal epilepsy studies. BBB water exchange is a promising noninvasive biomarker of BBB dysfunction in epilepsy. PLAIN LANGUAGE SUMMARY: The blood-brain barrier protects the brain from harmful substances while letting nutrients pass from the blood. In epilepsy, this barrier can become disrupted and may make seizures worse. We tested a noninvasive MRI method (no injections) to measure how well the blood and brain exchange substances. Our results show the technique can clearly visualize these exchanges and can be repeated reliably, offering a safe tool to study barrier function in people with epilepsy.