Li, Yinghao

Abstract Background Recently, a posterior pathway for fluid drainage from the retina to the meningeal lymphatics in the optic nerve (ON) sheath was identified in rodents using intravitreal imaging tracers directly injected into the ocular-globe. Fluid and solute clearance along this pathway may be associated with many diseases. However, intravitreal tracers are rarely used in clinical imaging. As intravenous Gadolinium-based-contrast-agent (GBCA) can enter the globe via the blood-ocular-barriers, it may provide an alternative approach to image this pathway. Purpose To establish a clinically feasible intravenous GBCA-based MRI approach for tracking fluid and solute transport along the posterior lymphatic pathway in the ocular glymphatic system. Materials&Methods This prospective study was conducted from March 2021 to September 2022 in healthy participants. Dynamic-susceptibility-contrast-in-the-CSF (cDSC) MRI was performed before, immediately and 4 hours after intravenous-GBCA administration to track GBCA distribution in aqueous humor (AH) and cerebrospinal fluid (CSF) in regions-of-interest (ROIs) in the globe (anterior-cavity, vitreous-body), in the intraorbital and extraorbital ON, and in the intracranial CSF space proximal to the ON (chiasmatic-cistern, interpeduncular-cistern). Kruskal–Wallis tests with post-hoc Dunn’s tests were used for group comparisons. Results Sixteen healthy participants (mean age±SD: 51±21 years, 5 men) were recruited. Intravenous-GBCA enhancement was observed in all ROIs immediately after injection. At 4-hour-post-GBCA, the vitreous body showed a trend of smaller enhancement area (55±11% versus 49±11%, P =.14) and lower GBCA-concentration (0.044±0.014 versus 0.028±0.010 mmol/L, P =.07) compared to immediate-post-GBCA. The intraorbital ON showed more widespread enhancement (39±5% versus 59±6%, P =.01) and significantly higher GBCA-concentration (0.023±0.009 versus 0.059±0.015 mmol/L, P <.001) at 4-hour-post-GBCA. Conclusion Dynamic fluid and solute transportation along the posterior lymphatic pathway in the ocular glymphatic system in healthy participants was measured by tracking intravenous-GBCAs entering the globe via the blood-ocular-barriers using cDSC-MRI. Summary Statement Dynamic fluid and solute transportation along the posterior lymphatic pathway in the ocular glymphatic system in healthy participants was measured by tracking intravenous-Gadolinium-based-contrast-agents entering ocular-globe via blood-ocular-barriers using dynamic-susceptibility-contrast-in-the-CSF (cDSC)-MRI. Key Results In this prospective study of sixteen participants, Gadolinium-based-contrast-agent (GBCA)-induced signal changes were detected in the aqueous-humor and cerebrospinal fluid immediately following intravenous administration using dynamic-susceptibility-contrast-in-the-CSF (cDSC)-MRI. At 4-hour-post-GBCA, the vitreous-body showed a trend of smaller enhancement area (55±11% versus 49±11%, P =.14) and lower GBCA-concentration (0.044±0.014 versus 0.028±0.010 mmol/L, P =.07) compared to immediate-post-GBCA. The intraorbital-optic-nerve showed more widespread enhancement (39±5% versus 59±6%, P =.01) and higher GBCA-concentration (0.023±0.009 versus 0.059±0.015 mmol/L, P <.001) at 4-hour-post-GBCA.

Dynamic fluid and solute transportation across the arachnoid barrier in the meninges of healthy participants was measured by tracking intravenous gadolinium-based contrast agent entering cerebrospinal fluid from dural blood vessels using dynamic dual-spin-echo perfusion MRI.

AbstractIron Dextran is a widely used iron oxide compound to treat iron‐deficiency anemia patients in the clinic. Similar to other iron oxide compounds such as Ferumoxytol, it can also be used off‐label as an intravascular magnetic resonance imaging (MRI) contrast agent due to its strong iron‐induced T2 and T2* shortening effects. In this study, we seek to evaluate the feasibility of using Iron Dextran enhanced multi‐echo susceptibility weighted imaging (SWI) MRI at 7T to image arterial and venous blood vessels in the human brain. Phantom experiments were performed to measure the r2* relaxivity for Iron Dextran in blood, based on which the SWI sequence was optimized. Pre‐ and post‐infusion MR images were acquired in human subjects from which maps of arteries and veins were extracted. The post‐contrast SWI images showed enhanced susceptibility difference between blood and the surrounding tissue in both arteries and veins. Our results showed that the proposed Iron Dextran enhanced multi‐echo SWI approach allowed the visualization of blood vessels with diameters down to ~100 μm, including small blood vessels supplying and draining small brain structures such as the hippocampus. We conclude that Iron Dextran can be an alternative iron‐based MRI contrast agent for blood vessel imaging in the human brain.