Manganese ion (Mn²⁺) is an intracellular contrast agent that enters viable myocardial cells via voltage gated calcium channels. Along with its T₁ shortening effect and relatively long half-life in cells, it becomes a very useful molecular contrast agent to study calcium influx. One major concern for using Mn²⁺ is getting quantitative information over a range of concentrations. Therefore, in this study, a T, mapping method has been implemented for cardiac manganese-enhanced MRI (MEMRI) to increase the sensitivity and enable the quantitative estimate of a range of concentrations.