Assessment of myocardial injury after reperfused infarction by T1ρ cardiovascular magnetic resonance
Stoffers RH, Madden M, Shahid M, Contijoch F, Solomon J, Pilla JJ, Gorman JH III, Gorman RC, Witschey WRT
Background: The evolution of T1ρ 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 T1ρ, T2 and T1 relaxation, scar size and transmurality at 1 week and 4 weeks post-MI.
Methods: 10 Yorkshire swine underwent 90 minutes of occlusion of the circumflex artery and reperfusion. T1ρ, T2 and native T1 maps and late gadolinium enhanced (LGE) MRI data were collected at 1 week (n=10) and 4 weeks (n=5). Semi-automatic FWHM 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 ΔT1 (infarct-remote) = 421.3 ± 108.8 (1 week) and 480.0 ± 33.2 ms (4 week), ΔT1ρ = 68.1 ± 11.6 and 74.3 ± 14.2, and ΔT2 = 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), CNRT1ρ = 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 T1ρ, 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 ΔT1ρ=-3.8%, ΔT1=- 3.5% and ΔLGE=-2.8% from 1 to 4 weeks, but there was no observed change in infarct size for T2 or histologically.
Conclusions: T1ρ 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.