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
Petitclerc, L.; Hirschler, L.; Wells, J.A.; Thomas, D.L.; Walderveen, M.A.A. van; Buchem, M.A. van; Osch, M.J.P. van 2021
The study of brain clearance mechanisms is an active area of research. While we know that the cerebrospinal fluid (CSF) plays a central role in one of the main existing clearance pathways, the... Show moreThe study of brain clearance mechanisms is an active area of research. While we know that the cerebrospinal fluid (CSF) plays a central role in one of the main existing clearance pathways, the exact processes for the secretion of CSF and the removal of waste products from tissue are under debate. CSF is thought to be created by the exchange of water and ions from the blood, which is believed to mainly occur in the choroid plexus. This exchange has not been thoroughly studied in vivo.We propose a modified arterial spin labeling (ASL) MRI sequence and image analysis to track blood water as it is transported to the CSF, and to characterize its exchange from blood to CSF. We acquired six pseudo-continuous ASL sequences with varying labeling duration (LD) and post-labeling delay (PLD) and a segmented 3D-GRASE readout with a long echo train (8 echo times (TE)) which allowed separation of the very long-T-2 CSF signal. ASL signal was observed at long TEs (793 ms and higher), indicating presence of labeled water transported from blood to CSF. This signal appeared both in the CSF proximal to the choroid plexus and in the subarachnoid space surrounding the cortex. ASL signal was separated into its blood, gray matter and CSF components by fitting a triexponential function with T(2)s taken from literature. A two-compartment dynamic model was introduced to describe the exchange of water through time and TE. From this, a water exchange time from the blood to the CSF (Tbl->CSF) was mapped, with an order of magnitude of approximately 60 s. Show less
