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BackgroundVisualization of aqueous humor flow in the human eye is difficult because gadolinium, a magnetic resonance imaging (MRI) contrast agent, does not readily cross the blood-retinal and blood-aqueous barriers of capillaries that supply water to the eye. The proton (1H) of oxygen-17 water (H217O) has a very short transverse relaxation time (T2), and the T2-weighted (T2W) 1H-MRI signal intensity of a region with H217O is lower than that with only H216O.PurposeTo observe the distribution of H217O in the human eye, and the flow into and out of the anterior chamber of H217O, using dynamic T2W 1H-MRI.Materials and MethodsSeven ophthalmologically normal adult volunteers under 40 years old participated in this study. During dynamic imaging, the subject self-administered 10 mol% H217O saline (0.92–1.37 mL) to their right eye for 1 min. Time-series images were created by subtracting the image before the eye drops from each of the images obtained after the eye drops. The “normalized signal intensity of the right anterior chamber” (rAC) in each image was obtained by dividing the signal intensity of the right anterior chamber region-of-interest by that of the left. Changes in transverse relaxation rate and H217O concentration (PO17) were calculated from the rAC. The inflow and outflow constants of H217O in the right anterior chamber were also determined.ResultsDecreased signal intensity after the H217O eye drops was observed in the anterior and posterior chambers, but not in the vitreous body. The rAC signal intensity decreased after the eye drops, and then recovered to close to rAC(0) at 40 min. The inflow and outflow constants were 0.53 ± 0.19 and 0.055 ± 0.019 min-1, respectively, and the peak value of PO17 was 0.19 ± 0.04% (mean ± SD).ConclusionH217O saline eye drops distributed in the human anterior and posterior chambers. Further, the eye drops smoothly flowed into, and slowly out of, the anterior chamber.SummaryO-17 water dropped into human eyes as a T2-weighted MRI contrast agent was distributed in the anterior and posterior chambers, with smooth flow into, and slow outflow from, the anterior chamber.Key findingsIn seven healthy volunteers, dynamic T2-weighted 1H-MRI showed that the signal intensity in the anterior chamber decreased smoothly after H217O eye drops and then slowly recovered, reaching a value close to that observed before the eye drops, after 40 minutes, with inflow and outflow constants of H217O of 0.53 ± 0.19 min-1 and 0.055 ± 0.019 min-1, respectively. The signal changes were limited to the anterior and posterior chambers and were not observed in the vitreous body. |
