Blood flow quantification of the human retina with MRI

The purpose of this study was to investigate the feasibility of measuring blood flow to the retina using arterial spin labeling MRI, a quantitative, noninvasive tomographic technique. Blood flow imaging was performed in a single axial slice through both eyes of five healthy volunteers with no history of retinal diseases. The imaging was optimized to minimize the errors from motion and nonuniform magnetic fields caused by proximity to the sinuses. Key hemodynamic factors for flow quantification, including arterial transit delay and the apparent decay time of the signal, were estimated by repeated measurements with different arterial spin labeling timing. A clearly elevated signal, consistent with the anatomical location of the retina, was observed in all subjects. The measured blood flow to a 1cm×1.47cm section of the retina, centered on the fovea, was 1.75±0.54μL/mm²/min (total blood flow of 261±87μL/min). The arterial transit delay from a labeling plane 5cm below the slice was 1137±288ms. These results establish the feasibility of measuring blood flow to the retina with MRI, and support the future characterization of the healthy and diseased ocular circulation with this method. The feasibility of measuring blood flow to the human retina using arterial spin labeling MRI on a clinical scanner was investigated in this study. Key hemodynamic factors for flow quantification were estimated by repeated measurements with different arterial spin labeling timing. The findings of this study establish the feasibility of measuring blood flow to the retina with MRI, and provide support for the future characterization of the healthy and diseased ocular circulation with this method.