Water exchange rate across the blood‐brain barrier is associated with CSF amyloid‐β 42 in healthy older adults

INTRODUCTION: We tested if water exchange across the blood‐brain barrier (BBB), estimated with a noninvasive magnetic resonance imaging (MRI) technique, is associated with cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease (AD) and neuropsychological function. METHODS: Forty cognitively normal older adults (67–86 years old) were scanned with diffusion‐prepared, arterial spin labeling (DP‐ASL), which estimates water exchange rate across the BBB (k(w)). Participants also underwent CSF draw and neuropsychological testing. Multiple linear regression models were run with k(w) as a predictor of CSF concentrations and neuropsychological scores. RESULTS: In multiple brain regions, BBB k(w) was positively associated with CSF amyloid beta (Aβ)42 concentration levels. BBB k(w) was only moderately associated with neuropsychological performance. DISCUSSION: Our results suggest that low water exchange rate across the BBB is associated with low CSF Aβ42 concentration. These findings suggest that k(w) may be a promising noninvasive indicator of BBB Aβ clearance functions, a possibility which should be further tested in future research.