On the origin of a potential clearance marker: The contribution of enlarged perivascular fluid diffusion to an MRI derived proxy of interstitial fluid

IntraVoxel Incoherent Motion (IVIM) MRI can detect the diffusion of cerebral interstitial fluid (ISF) (D int) and its volume fraction (f int), which has the potential as a proxy of cerebral waste clearance. fint has been suggested to both be driven by fluid diffusivity within enlarged perivascular spaces (ePVS) ‐ transporting fluid from the subarachnoid space into the parenchyma ‐ and the ISF between the parenchymal cells. Both factors play a crucial role in soluble protein clearance, e.g., Amyloid‐Beta (Aβ).