Normal and infarcted myocardium: Differentiation with cellular uptake of manganese at MR imaging in a rat model

Purpose: To assess whether normal myocardium can be distinguished from infarction at magnetic resonance (MR) imaging with low doses of manganese dipyridoxyl diphosphate (Mn-DpDp). Materials and methods: After 1-hour coronary arterial occlusion and 2-hour reperfusion, three groups of eight rats each were injected with 25, 50, or 100 mu mol of Mn-DpDp per kilogram of body weight. The longitudinal relaxation rate (R1) in normal myocardium, reperfused infarction, and blood was repeatedly measured at inversion-recovery echo-planar imaging before and for 1 hour after the administration of contrast material. Afterward, several animals from each group were examined at high-spatial-resolution inversion-recovery spin-echo (SE) Mr imaging. Results: Manganese accumulated in normal myocardium but was cleared from reperfused infarction and blood. One hour after the administration of Mn-DpDp, R1 in normal myocardium (1.53 sec(-1) +/- 0.03, 1.73 sec(-1) +/- 0.03, and 1.94 sec(-1) +/- 0.02, respectively, for 25, 50, and 100 mu mol/kg) was significantly (P < 0.5) faster than that of reperfused infarction (0.99 sec(-1) +/- 0.03, 1.11 sec(-1) +/- 0.03, and 1.48 sec(-1) +/- 0.06). Normal myocardium appeared hyperintense on T1-weighted inversion-recovery SE MR images and was clearly distinguishable from reperfused infarction. Conclusion: Mn-DPDP-enhanced inversion-recovery echo-planar and SE MR images demonstrated retention of manganese in normal myocardium and clearance of manganese from infarction. Mn-DPDP has characteristics similar to those of widely used thallium and may be useful in the assessment of myocardial viability at MR imaging.