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 diffusion-weighted MRI at 4.7 Tesla was performed. Layer-specific thickness, T₂, spin density, apparent diffusion coefficient perpendicular (ADC_⊥) and parallel (ADC _∥) to the retinal surface were tabulated. T₁-weighted MRI was acquired before and after Intravenous 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 T₂, 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 enhancement) overlapped the photoreceptor cell layer and the inner and outer segments. The outer strip (exhibiting large T₂, ADC, spin density with Gd-DTPA enhancement) overlapped the tapetum and choroidal vascular layer. T₂, spin density, ADC_⊥ and ADC_∥ 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 ± 13μm (N = 6) by MRI and 319 ± 77 μm (N = 5) by histology. Conclusion: MRI provides a noninvasive tool to study the retina with laminar specificity without depth limitation.