The blood-brain barrier (BBB) and blood-CSF barrier (BCSFB) are crucial structures which regulate the transport of water and other molecules between the blood and brain tissue or fluids. This work... Show moreThe blood-brain barrier (BBB) and blood-CSF barrier (BCSFB) are crucial structures which regulate the transport of water and other molecules between the blood and brain tissue or fluids. This work investigates the use of arterial spin labeling (ASL) MRI to characterize the exchange of water from blood to tissue and cerebrospinal fluid (CSF). We describe multi-time-point and multi-echo ASL protocols which allow the tracking of a bolus of blood water through the vasculature and beyond, and to separate the origin of the signal based on he T2 of different compartments. We find that blood-to-CSF water exchange occurs at a much slower rate (approx. 100-fold) than blood-to-GM. Blood-to-CSF water exchange was also observed in both the choroid plexus which is the source of production of CSF, and in the subarachnoid space that surrounds the brain tissue. We discuss the implications of this finding for our understanding of CSF production and brain waste clearance. Show less