Table 3.
Analytic method used in the glymphatic assessment of each sequence.
| Group | Source | Subj. vs. Obj. | Targeted anatomical structures | Time-point dynamic enhancement and peak enhancement time | Flow change and direction | |||
|---|---|---|---|---|---|---|---|---|
| CSF | Parenchyma | MLV | Cervical LNs | |||||
| Contrast-enhancement MRI group | Absinta et al. (8) | Subj. | No | No | Yes (5 of 5) | No | NA | NA |
| Eide et al. (9) | Obj. | Yes (near IFG after 4–9 h in 13 of 16 individuals) | Yes (IFG (in 14 of 15)*, PHG, thalamus, and pons after 24–48 h) | No | Yes (LN after 24–48 h in 9 of 15* individuals) | Peak glymphatic enhancement occurred within the CSF space (near IFG) and brain parenchyma (IFG) on T1WI after 4–6 h and 24–48 h | NA | |
| Jacobsen et al. (10) | Obj. | Yes (prechiasmatic cistern after 4–6 h) |
Yes (optic nerve, optic chiasm, optic tract, and primary visual cortex after 24 h, except optic chiasm (6–9 h)) |
No | No | Peak glymphatic enhancement occurred within the CSF (prechiasmatic cistern) and brain parenchyma of visual pathway (optic nerve, optic tract, and primary visual cortex) on T1WI after 4–6 h and 24 h | NA | |
| Naganawa et al. (13) | Subj | Yes (around the cortical veins after 4 h in 155 of 190 individuals) |
No | No | No | Glymphatic enhancement occurred within the CSF space around the cortical vein on FLAIR after 4 h | NA | |
| Oner et al. (14) | Subj. & Obj. | No | Yes (globus pallidus and dentate nucleus in 5 of 6 individuals/ Increment of signal intensity ratio within brain parenchyma on T1WI (in 6 of 6))† |
No | No | Glymphatic enhancement occurred within the brain parenchyma (dentate nucleus and globus pallidus) on T1WI | NA | |
| Ringstad et al. (16) | Obj. | Yes (foramen magnum (1–2 h), pontine cistern (1–2 h), Sylvian fissure (4–6 h), 3rd and 4th ventricles (4–6 h), central sulcus (4–6 h), and lateral ventricle (6–9 h), and after <9 h) |
Yes (IFG, pons, thalamus, frontal horn, and precentral gyrus after 24 h) |
No | No | Peak glymphatic enhancement occurred within all CSF spaces and brain parenchyma (IFG) on T1WI after <9 h and 24 h | NA | |
| Zhou et al. (17) | Obj. | Yes (4th (in 10 of 14), 3rd (in 9 of 14), and lateral ventricles (in 9 of 14) after 4.5 h) |
Yes (frontal horn (in 10 of 14), IFG (in 11 of 14), and precentral gyrus (in 12 of 14) after 15 h) |
Yes (after 15 h in 9 of 14 individuals) |
Yes (cervical LN after 39 h in 2 of 2* individuals) |
Peak glymphatic enhancement occurred within CSF space (fourth ventricle), brain parenchyma (precentral gyrus) on FLAIR after 4.5 h and 15 h | NA | |
| Non-contrast MRI group | Kiviniemi et al. (11) | Obj. | Yes (periarterial) |
Yes | Yes (perivenous) | No | NA | Glymphatic flows were demonstrated within the brain parenchyma on MREG (arterial pulsei induced glymphatic flow from the CSF spaces to the brain parenchyma and venous flow induce glymphatic flow from the brain parenchyma to MLV) |
| Kuo et al. (12) | Subj. | No | No | Yes (alongside the SSS in 6 of 6 individuals) |
No | NA | Glymphatic flows were demonstrated within MLV on TOF MRA (MLV had countercurrent flow to venous flow) | |
| Rajna et al. (15) | Obj. | Yes | Yes | Yes | No | NA | Glymphatic flows were demonstrated within the brain parenchyma on MREG (arterial pulse induced glymphatic flow from CSF spaces to the brain parenchyma) | |
ACA, anterior cerebral artery; CSF, cerebrospinal fluid; fluid-attenuated inversion recovery (FLAIR); h, hours; IFG, inferior frontal gyrus; LN, lymph node; MCA, middle cerebral artery; min, minutes; MLV, meningeal lymphatic vessels; MREG, magnetic resonance encephalography; NA, not applicable; PCA, posterior cerebral artery; PHG, parahippocampal gyrus; pre., precontrast; Obj., objective signal quantification; SSS, superior sagittal sinus; sub., subjective visual assessment; T1WI, T1-weighted imaging; TOF MRA, time-of-flight MR angiography.
The number of parent patients was not the same as the original enrolled number of patients because the peak enhancement can only be evaluated in the person who showed positive signal unit changes [18 (not 19) in the parenchyma and 17 (not 19) in the cervical LN in Eide et al. (9), and 2 (not 14) in the cervical LN in Zhou et al. (17)].
The increments of the globus pallidus-to-thalamus signal intensity ratio and the dentate nucleus-to-pons signal intensity ratio were evaluated between the initial unenhanced T1WI and control non-enhanced T1WI after performing contrast-enhanced MRC.