Assessment of myocardial injury after reperfused infarction by T1ρ cardiovascular magnetic resonance

Background: The evolution of T1 rho and of other endogenous contrast methods (T2, T1) in the first month after reperfused myocardial infarction (MI) is uncertain. We conducted a study of reperfused MI in pigs to serially monitor T1 rho, T2 and T1 relaxation, scar size and transmurality at 1 and 4 weeks post-MI. Methods: Ten Yorkshire swine underwent 90 min of occlusion of the circumflex artery and reperfusion. T1 rho, T2 and native T1 maps and late gadolinium enhanced (LGE) cardiovascular magnetic resonance (CMR) data were collected at 1 week (n = 10) and 4 weeks (n = 5). Semi-automatic FWHM (full width half maximum) thresholding was used to assess scar size and transmurality and compared to histology. Relaxation times and contrast-to-noise ratio were compared in healthy and remote myocardium at 1 and 4 weeks. Linear regression and Bland-Altman was performed to compare infarct size and transmurality. Results: Relaxation time differences between infarcted and remote myocardial tissue were.T1 (infarct-remote) = 421.3 +/- 108.8 (1 week) and 480.0 +/- 33.2 ms (4 week), Delta T1 rho = 68.1 +/- 11.6 and 74.3 +/- 14.2, and Delta T2 = 51.0 +/- 10.1 and 59.2 +/- 11.4 ms. Contrast-to-noise ratio was CNRT1 = 7.0 +/- 3.5 (1 week) and 6.9 +/- 2.4 (4 week), CNRT1 rho = 12.0 +/- 6.2 and 12.3 +/- 3.2, and CNRT2 = 8.0 +/- 3.6 and 10.3 +/- 5.8. Infarct size was not significantly different for T1 rho, T1 and T2 compared to LGE (p = 0.14) and significantly decreased from 1 to 4 weeks (p < 0.01). Individual infarct size changes were Delta T1 rho = -3.8%, Delta T1 = -3.5% and Delta LGE = -2.8% from 1 -4 weeks, but there was no observed change in infarct size for T2 or histologically. Conclusions: T1 rho was highly correlated with alterations left ventricle (LV) pathology at 1 and 4 weeks post-MI and therefore it may be a useful method endogenous contrast imaging of infarction.