Magnetic resonance imaging of tissue and vascular layers in the cat retina

Purpose: To report the visual resolution of multiple cell and vascular "layers" in the cat retina using MRI. Materials and Methods: T-2- and diffuston-weighted MRI at 4.7 Tesla was performed. Layer-specific thickness, T-2, spin density, apparent diffusion coefficient perpendicular (ADC(perpendicular to)) and parallel (ADC) to the retinal surface were tabulated. T-1-weighted MRI was acquired before and after intraverious administration of Gd-DTPA and subtraction images were obtained, Histology was performed for validation. Results: Three distinct "layers" were observed. The inner strip nearest to the vitreous (exhibiting large T-2, ADC, spin density with Gd-DTPA enhancement) overlapped the ganglion cell layer, bipolar cell layer, and the embedded retinal vascular layer. The middle strip (exhibiting small T-2, ADC, spin density without Gd-DTPA enhancernent) overlapped the photoreceptor cell layer and the inner and outer segments. The outer strip (exhibiting large T2, ADC, spin density with GdDTPA enhancement) overlapped the tapetum and choroidal vascular layer. T-2, spin density, ADC(perpendicular to) and ADC(parallel to) of different "layers" were tabulated. The inner strip was slightly thicker than the other two strips. The total thickness, including neural and nonneural retina, was 358 +/- 13 mu m (N = 6) by MRI and 319 +/- 77 mu m (N = 5) by histology. Conclusion: MRI provides a noninvasive tool to study the retina with laminar specificity without depth limitation.