Relaxation-exchange imaging (REXI) for the measurement of trans-barrier water exchange in choroid plexus

Motivation: Scarcity of non-invasive imaging techniques of choroid plexus function hindered our knowledge of the blood-cerebrospinal fluid barrier (BCSFB). Goal(s): We aimed to measure the trans-barrier water exchange rate in choroid plexus. Approach: We developed a new imaging method and contrast mechanism, named relaxation-exchange imaging (REXI), and validated its feasibility on both phantoms and rats. Results: REXI successfully captured the changes in proton exchange rate of urea-water phantoms at varying pH. In-vivo experiments on rats showed the potential of REXI to measure the trans-barrier water exchange in choroid plexus. Impact: Given the emerging importance of neurofluids and choroid plexus, our novel MRI method REXI provides a way to measure the trans-barrier water exchange in CP and a potential imaging tool to evaluate CP function in future studies.