Relaxation enhancing properties of MnDPDP in human myocardium

PURPOSE To assess magnitude and duration of changes in myocardial longitudinal relaxation rate (R1) in humans following infusion of the manganese (Mn) releasing contrast agent MnDPDP (Mn-dipyridoxyl-diphosphate). MATERIALS AND METHODS Fifteen healthy volunteers were divided into three groups. After initial myocardial and liver R1 measurements using an inversion recovery (IR) turbo fast low-angle shot (FLASH) sequence at 1.5 Tesla, the groups were given different doses of intravenous MnDPDP: 5, 10 and 15 mol/kg body weight, respectively, over 30 minutes. R1 measurements were then repeated at 1, 2, 4, 8, and 24 hours after the infusion ended. RESULTS The left ventricular wall R1 prevalue was 0.98 second-1 (±0.04). R1 increased on average (all 15 subjects) 0.41 second-1 (±0.09). The increase was present one hour after the end of the infusion, remained relatively constant the next two hours, and then declined gradually. After 24 hours, there was still a moderate R1 elevation present, with an average R1-value of 1.16 (±0.05). There were only small differences in myocardial R1 responses between the three doses investigated, which was contrasted by a marked dose-response in liver tissue. CONCLUSION MnDPDP gave a significant and prolonged rise in myocardial R1 even at a dose of 5 mol/kg. The R1-values in the myocardium did not increase linearly with higher doses.