Fig. 1

Schematic of the glymphatic system (upper row) and MRI-based noninvasive methods (Bottom row). Briefly, from arteries, cerebrospinal fluid (CSF) crosses the perivascular space entering the interstitium through the AQP-4 channel and moving toward perivenous spaces (zigzag arrow). Although formal validation studies are still lacking, we hypothesized that PVS may serve as a proxy for periarterial flow; deterioration in the exchange of CSF and interstitial fluid would increase the extracellular fractional volume of free water (FW); DTI-ALPS measures the diffusivity capacity of the perivenous space surrounding the deep medullary vein at the lateral ventricle body level, enabling the assessment of the CSF outflow channel within this system. Abbreviation: PVS, perivascular space; AQP-4, aquaporin-4; DTI-ALPS, Diffusivity Along the Perivascular Spaces