Early T1 Myocardial MRI Mapping: Value in Detecting Myocardial Hyperemia in Acute Myocarditis

Background: Hyperemia is a key component of acute myocarditis (AM). Early gadolinium uptake because of myocardial hyperemia may be quantified by using T1 mapping. Purpose: To evaluate the value of early enhanced T1 shortening for the diagnosis of acute myocarditis. Materials and Methods: Study participants suspected of having AM and healthy control (HC) participants were prospectively enrolled from September 2016 to May 2019. Participants underwent 1.5-T cardiac MRI including Lake Louise criteria, T2 mapping, native T1, and extracellular volume, with the addition of early enhanced T1 mapping (2 minutes after intravenous administration of 0.15 mmol/kg gadobutrol). Color-coded maps of the percentage of T1 shortening from precontrast to early postcontrast were generated. Optimal early T1 shortening cut-off value and its diagnostic performance in the identification of acute myocarditis were calculated. Results: Forty-five study participants with AM (median age, 40 years; interquartile range [IQR], 20-46 years; 22 women) diagnosed according to multidisciplinary clinical evaluation, electrocardiography, laboratory test, echocardiography, cardiac MRI, and coronary CT and/or invasive angiography. Findings were confirmed by endomyocardial biopsy in 64% (29 of 45) of participants. MRI parameters were compared with 19 HC participants (median age, 39 years; IQR, 28-46 years; seven women). Median early T1 shortening was 75% (IQR, 72%-78%) in participants with AM versus 65% (IQR, 61%-66%) in HC participants (P < .001). Early T1 shortening showed high diagnostic performance (area under the receiver operating characteristic curve [AUC], 0.97; 95% confidence interval [CI]: 0.94, 1.00) and excellent interobserver reproducibility (intraclass correlation coefficient: 0.98; 95% CI: 0.96, 1.00). Early T1 shortening of 70% or greater identified acute myocarditis with 93% sensitivity, 100% specificity, and 95% diagnostic accuracy. Early T1 shortening had better diagnostic performance than late percentage T1 shortening (AUC, 0.97 vs 0.90, respectively; P = .03) and extracellular volume (AUC, 0.97 vs 0.88, respectively; P = .046), and similar to native T1 (AUC, 0.97 vs 0.93, respectively; P = .63) and T2 mapping (AUC, 0.97 vs 0.97, respectively; P > .99). Conclusion: In this proof-of-concept study, percentage of T1 shortening at early enhanced T1 mapping showed high accuracy for the diagnosis of acute myocarditis. (C) RSNA, 2020