Histological Validation of Cardiovascular Magnetic Resonance T1 Mapping for Assessing the Evolution of Myocardial Injury in Myocardial Infarction: An Experimental Study

Objective: To determine whether T1 mapping could monitor the dynamic changes of injury in myocardial infarction (MI) and be histologically validated. Materials and Methods: In 22 pigs, MI was induced by ligating the left anterior descending artery and they underwent serial cardiovascular magnetic resonance examinations with modified Look-Locker inversion T1 mapping and extracellular volume (ECV) computation in acute (within 24 hours, n = 22), subacute (7 days, n = 13), and chronic (3 months, n = 7) phases of MI. Masson's trichrome staining was performed for histological ECV calculation. Myocardial native T1 and ECV were obtained by region of interest measurement in infarcted, peri-infarct, and remote myocardium. Results: Native T1 and ECV in peri-infarct myocardium differed from remote myocardium in acute (1181 +/- 62 ms vs. 1113 +/- 64 ms, p = 0.002; 24 +/- 4% vs. 19 +/- 4%, p = 0.031) and subacute phases (1264 +/- 41 ms vs. 1171 +/- 56 ms, p < 0.001; 27 +/- 4% vs. 22 +/- 2%, p = 0.009) but not in chronic phase (1157 +/- 57 ms vs. 1120 +/- 54 ms, p = 0.934; 23 +/- 2% vs. 20 +/- 1%, p = 0.109). From acute to chronic MI, infarcted native T1 peaked in subacute phase (1275 +/- 63 ms vs. 1637 +/- 123 ms vs. 1471 +/- 98 ms, p < 0.001), while ECV progressively increased with time (35 +/- 7% vs. 46 +/- 6% vs. 52 +/- 4%, p < 0.001). Native T1 correlated well with histological findings (R-2 = 0.65 to 0.89, all p < 0.001) so did ECV (R-2 = 0.73 to 0.94, all p < 0.001). Conclusion: T1 mapping allows the quantitative assessment of injury in MI and the noninvasive monitoring of tissue injury evolution, which correlates well with histological findings.