The glymphatic system clears metabolic waste from the brain and can be probed using contrast-enhanced MRI. We investigated whether early-phase gadolinium-based contrast agent (GBCA) uptake varies with time of day and age. In this retrospective study, 447 patients who underwent brain MRI for suspected movement disorders received pre- and post-contrast T1 mapping a median of 5.9 minutes after GBCA injection. Scans were categorized as daytime (n = 307) or nighttime (n = 140). Regional ΔT1 values were measured in the cerebral and cerebellar cortices, white matter, basal ganglia perivascular spaces, and choroid plexus. Daytime cohorts showed significantly greater cortical enhancement than nighttime cohorts, particularly in the frontal, parietal, and temporal lobes, while no differences were observed in white matter, perivascular spaces, or choroid plexus. Increasing age was independently associated with stronger cortical enhancement across both day and night scans, with no significant interaction between age and time. These findings suggest that cortical GBCA retention is influenced by both circadian timing and aging, supporting early-phase T1 mapping as a practical approach to evaluate human glymphatic function.
Lee et al. (2026) studied this question.