T1 mapping for assessment of myocardial injury and microvascular obstruction at one week post myocardial infarction

Abstract Objectives To compare 3T T1 mapping to conventional T2 -weighted (T2 W) imaging for delineating myocardial oedema one week after ST-elevation myocardial infarction (STEMI), and to explore the confounding effects of microvascular obstruction (MVO) on each technique. Methods T2 W spectral attenuated inversion recovery and native T1 mapping were applied in 10 healthy volunteers and 62 STEMI patients, and late gadolinium enhancement was included for infarct localisation at 1 week and at 6 months post-STEMI. Segmental T1 values and T2 W signal intensity ratios were calculated; oedema volumes and salvage indices were determined in patients using image thresholding—a receiver operator characteristic (ROC) derived T1 threshold, and a 2SD T2 W threshold; and the results were compared between patients with/without MVO ( n = 35/27). Results Native T1 mapping delineated oedema with significantly better discriminatory power than T2 W—as indicated by ROC analysis (area-under-the-curve, AUC = 0.89 versus 0.83, p = 0.009; and sensitivity/specificity = 83/83% versus 73/73%). The optimal ROC threshold derived for T1 mapping was 1241 ms, which gave significantly larger oedema volumes than 2SD T2 W ( p = 0.006); with this threshold, patients with and without MVO showed similar oedema volumes, but patients with MVO had significantly poorer salvage indices ( p < 0.05) than those without. Neither method was significantly affected by MVO, the volume of which was seen to increase exponentially with infarct size. Conclusions Native T1 mapping at 3T can delineate oedema one week post-STEMI, showing larger oedema volumes and better discriminatory power than T2 W imaging, and it is suitable for quantitative thresholding. Both techniques are robust against MVO-related magnetic susceptibility.