Figure 5. Schemes of waste clearance. A: Schematic of waste clearance in body tissue outside the brain. B: Schematic of CWC illustrating the participation of both the venous system and CSF system; The main difference between CWC and body waste clearance is the extra layer of CSF (red dashed line in B). C: Illustration of the one-way transfer of cerebral waster from the brain parenchyma to capillaries or venules as well as much smaller diameter of the para-venous pathway comparing to the corresponding venous pathway, which makes it less effective in waste clearance anatomically.

Figure 4. Participation of the parenchymal venous pathway in CWC. SWI signal intensity changes post-SPIO CSF tracer infusion in normal rats. A-B: Quantitative MRI signal intensity changes pre-/post-low dose 75μg (A) and high dose 270 μg (B) FeREX (100nm) in azp and azicv; demonstrating CSF tracer presence in azicv, but not azp, at low dose. C-D: Quantitative MRI signal intensity changes pre-/post-low dose 75μg (C) and high dose 240 μg (D) Ferumoxytol (21nm) in azp and azicv; demonstrating CSF tracer presence in azicv, but not azp, at low dose.