Relationship between blood and myocardium manganese levels during manganese‐enhanced MRI (MEMRI) with T 1 mapping in rats

Manganese ions (Mn 2+ ) enter viable myocardial cells via voltage‐gated calcium channels. Because of its shortening of T 1 and its relatively long half‐life in cells, Mn 2+ can serve as an intracellular molecular contrast agent to study indirect calcium influx into the myocardium. One major concern in using Mn 2+ is its sensitivity over a limited range of concentrations employing T 1 ‐weighted images for visualization, which limits its potential in quantitative techniques. Therefore, this study assessed the implementation of a T 1 mapping method for cardiac manganese‐enhanced MRI to enable a quantitative estimate of the influx of Mn 2+ over a wide range of concentrations in male Sprague‐Dawley rats. This MRI method was used to compare the relationship between T 1 changes in the heart as a function of myocardium and blood Mn 2+ levels. Results showed a biphasic relationship between ΔR 1 and the total Mn 2+ infusion dose. Nonlinear relationships were observed between the total Mn 2+ infusion dose versus blood levels and left ventricular free wall ΔR 1 . At low blood levels of Mn 2+ , there was proportionally less cardiac enhancement seen than at higher levels of blood Mn 2+ . We hypothesize that Mn 2+ blood levels increase as a result of rate‐limiting excretion by the liver and kidneys at these higher Mn 2+ doses. Copyright © 2010 John Wiley & Sons, Ltd.