Improve myocardial T₁ measurement in rats with a new regression model: Application to myocardial infarction and beyond

Purpose To improve myocardial and blood T₁ measurements with a multi-variable T₁ fitting model specifically modified for a segmented multi-shot FLASH sequence. Methods The proposed method was first evaluated in a series of phantoms simulating realistic tissues, and then in healthy rats (n = 8) and rats with acute myocardial infarction (MI) induced by coronary artery ligation (n = 8). Results By taking into account the saturation effect caused by sampling α-train pulses, and the longitudinal magnetization recovery between readouts, our model provided more accurate T₁ estimate than the conventional three-parameter fit in phantoms under realistic gating procedures (error of -0.42 ± 1.73% versus -3.40 ± 1.46%, respectively, when using the measured inversion efficiency, β). The baseline myocardial T₁ values in healthy rats was 1636.3 ± 23.4 ms at 7 Tesla. One day postligation, the T₁ values in the remote and proximal myocardial areas were 1637.5 ± 62.6 ms and 1740.3 ± 70.5 ms, respectively. In rats with acute MI, regional differences in myocardial T₁ values were observed both before and after the administration of gadolinium. Conclusion The proposed method has improved T₁ estimate as validated in phantoms and could advance applications in rodents using quantitative myocardial T₁ mapping. Magn Reson Med 72:737-748, 2014.