Toward clinical application of manganese-enhanced MRI of retinal function

PurposeThe application of manganese-enhanced MRI (MEMRI) to measure retinal function in humans is unclear. To begin to address this gap, we tested the hypothesis that an FDA-approved manganese-based MRI contrast agent, Teslascan, is useful for measuring functional intraretinal ionic regulation.MethodsAnesthetized dark- or light-adapted male healthy Sprague–Dawley rats were infused for 30 min with 10 μmol/kg of Teslascan (clinically relevant dose; n = 5), 100 μmol/kg Teslascan (n = 5), or saline (n = 5). Four hours post-administration, high resolution MEMRI data were collected. Intraretinal signal intensities and enhancements were measured. Modelling was performed to estimate apparent retinal transfer constant Ki and to determine optimal data acquisition parameters.ResultsIn light-adapted rats, intraretinal enhancements responded in a dose–response manner. In addition, in the outer retina the effect of light-adaptation was to reduce significantly Mn2+ uptake and Ki compared to dark-adaptation. A non-significant change was also observed in the inner retina. Modelling shows Mn2+ plasma concentration reaching a plateau after about 2 h. Apparent Ki values for the clinically relevant dose are 3–6 × 10−3 min−1, decreasing to 0.5–0.6 × 10−3 min−1 at the higher dose. Intraretinal signal is almost linear with Ki. Optimal TR for a spin-echo sequence is 0.4–1.4 s.ConclusionFirst time evidence is presented that a clinically relevant dose and route of Teslascan can be used to measure intraretinal function. The potential for future clinical application of MEMRI in a broad range of retinopathies is high.