Non-invasive characterization of perivascular subarachnoid spaces.

Cerebrospinal fluid (CSF) is thought to facilitate brain waste clearance and immune surveillance, yet its compartmentalization remains unclear. Previous work, using invasive dynamic intrathecal MRI contrast imaging, identified a perivascular subarachnoid space (PVSAS) that enhances along the major cerebral arteries with a 'donut'-like appearance. These findings suggest that the PVSAS may be separated from the surrounding broader subarachnoid space (SAS) by a semipermeable perivascular membrane. To investigate if the PVSAS could be observed non-invasively in healthy controls, we used a magnetic resonance imaging technique, CSF-STREAM (CSF-Selective T2-prepared REadout with Acceleration and Mobility-encoding), that assesses CSF-mobility at a high spatial resolution by isolating CSF from blood and tissue signal. Here, we observe high CSF-mobility next to the vasculature, with a steep drop-off into the surrounding SAS around both the middle and anterior cerebral arteries, suggesting the presence of the PVSAS in healthy controls. We find that CSF dynamics may be more spatially distinct than previously thought, providing a possible foundation for understanding brain CSF patterns in health and disease.