Original Research Manganese-Enhanced MRI Reveals Multiple Cellular and Vascular Layers in Normal and Degenerated Retinas

nance imaging (MEMRI) at 25 25 800 mm3 to image different retinal and vascular layers in the rat retinas. Materials and Methods: Manganese-chloride was injected intraocularly in normal (n 5) and Royal College of Surgeons (RCS, an model of photoreceptor degenera-tion) (n 5) rats at postnatal day 90. MEMRI at 4.7 T was performed 24 hours later. MRI was repeated following intravenous Gd-DTPA in the same animals to highlight the vasculatures. Layer assignment and thickness were compared to histology. Results: MEMRI 24 hours after intravitreal manganese-chloride injection revealed seven bands of alternating hyper- and hypointensities, corresponding histologically to the ganglion cell layer, inner plexiform layer, inner nu-clear layer, outer plexiform layer, outer nuclear layer, photoreceptor-segment layer, and choroidal vascular layer. Intravenous Gd-DTPA—which does not cross the blood–retinal barrier and the retinal pigment epithelium— further enhanced the two layers bounding the retina, cor-responding to the retinal and choroidal vascular layers, but not the avascular outer nuclear layer and the photo-receptor-segment layer. MEMRI of the RCS retinas revealed the loss of the outer plexiform layer, outer nu-clear layer, and photoreceptor-segment layer. Histological analysis corroborated the MRI laminar assignments and thicknesses. Conclusion: Lamina-specific retinal structures neurode-generative changes to structure in retinal diseases can be detected using MEMRI