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Shu-Wei Sun, Bruce Campbell, Chantal Lunderville, Eric Won, Hsiao-Fang Liang; Noninvasive Topical Loading for Manganese-Enhanced MRI of the Mouse Visual System. Invest. Ophthalmol. Vis. Sci. 2011;52(6):3914-3920. doi: 10.1167/iovs.10-6363.
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To evaluate topical loading as an alternative to intravitreal injection for Mn2+-enhanced magnetic resonance imaging (MEMRI) of the visual system.
Topical administration of 0.5 to 1.5 M MnCl2 and intravitreal injections with 0.5 μL 100 mM and 2 μL 1 M MnCl2 for mouse MEMRI were conducted, followed by immunohistochemistry. In another mouse group, two topical administrations of 1 M Mn2+ were applied to the same animals 7 days apart, to evaluate the use of MEMRI in a time course study. Dynamic imaging was also conducted to reveal how Mn2+ travels to the retina. MEMRI with topically loaded MnCl2 was also conducted in eyes with retinal ischemia, to evaluate whether the enhancements required healthy neurons.
After 1 day, topical administration of 1 M and 1.5 M MnCl2 rendered significant signal enhancement (up to 20%) in the superior colliculus (P < 0.05) that was equivalent to that of the 2-μL 1 M injection. Repeated exposure to Mn2+ showed reproduced enhancement. Dynamic imaging showed significant enhancement in the iris, retina, and lens boundary, but not in the vitreous space. In retinal ischemic eyes, no enhancement of MEMRI was detected in the optic nerves. The immunohistochemistry of the optic nerve (1.5 mm anterior to the chiasm) and retina showed no injury 1 week after Mn2+ topical administrations to each mouse.
The results demonstrated the feasibility of using topical administration of Mn2+ for MEMRI. Topically loaded Mn2+ did not diffuse into the vitreous space, but was it may have been absorbed into the iris to diffuse or travel via the capillary circulation to reach the retina.
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