SODIUM MRI & CSI OF EXPERIMENTAL DIABETIC RETINOPATHY

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The specific aim of the proposed research is to use sodium magnetic resonance imaging (23Na MRI) and sodium chemical shift imaging (23Na CSI) to characterize the state of the vitreous body in two animal models of diabetic retinopathy. Diabetic retinopathy, a complication of diabetes, is the major cause of new blindness in persons between the ages of 25 and 35 years, and continues to grow in importance as medical advances extend the longevity of diabetics. The increasing number of diabetic blind, especially in the juvenile onset category, offers a clear challenge to develop effective strategies for the basic understanding, diagnoses and treatment of this disorder. Magnetic resonance has proven to be an excellent tool for the study of sodium because of the high contrast obtainable in 23Na magnetic resonance images, the inherent sensitivity of this quadrupolar nucleus to its environment, and the relatively high concentration of sodium in biological systems. In this work we will use sodium magnetic resonance imaging and chemical shift imaging techniques developed by the principal investigator and her students and collaborators to investigate the effects of diabetic retinopathy on the vitreous body by: 1. measuring, on a local basis within the vitreous, sodium spin-spin relaxation times and sodium "visibility"; 2. assessing leakage of blood constituents across the blood-retinal barrier by monitoring the flow of intravenously administered paramagnetic shift reagent into the vitreous. Diabetic retinopathy will be modeled by laster photocoagulation of the retina and by alloxan induction of diabetes. We anticipate that blood- retinal barrier dysfunction will result in chemical shift images of the regions of the vitreous distinct from those of normal vitreous. We also anticipate that sodium spin-spin relaxation times and visibility values will change as the state of the vitreous is altered through the leakage of blood constituents from retinal blood vessels. These parameters will provide insight into the changing nature of the vitreous gel associated with diabetic retinopathy.