Native T1 relaxation times hold potential for acute myocarditis imaging

Native T1 relaxation times have the potential to complement current cardiac MR approaches in patients suspected of having acute myocarditis, according to a study published online June 6 by Radiology.

Cardiac MRI is an established noninvasive diagnostic tool for the detection of acute and chronic myocarditis. Diagnosis is made at 1.5-T and is based on the “Lake Louise” criteria for assessing myocardial inflammation using cardiac MR, but the criteria have several disadvantages, including limitations due to signal intensity inhomogeneities and the fact it can only facilitate qualitative visual assessment.

Because of these hindrances, a quantitative imaging technique that can be performed during breath hold to minimize respiratory motion artifacts would be ideal. A technique for noninvasive tissue characterization based on calculation of myocardial T1 relaxation times and T1-derived volume fraction (ECV) has been developed, and lead author Julian A. Luetkens, MD, of the University of Bonn in Germany, and colleagues evaluated the diagnostic value of cardiac MRI at 3 T in patients suspected of having acute myocarditis by using a multiparametric cardiac MRI approach including T1 relaxation times as an additional tool for tissue characterization.

The study included 24 patients with acute myocarditis and 42 control subjects. Cardiac MRI approaches used in the study were as follows: relative T2 short tau inversion-recovery signal intensity ratio, early gadolinium enhancement ratio, late gadolinium enhancement, native T1 relaxation times and extracellular volume fraction.

Results revealed that native T1 relaxation times were significantly longer in patients with acute myocarditis than in the control subjects, as the times were 1185.3 msec versus 1089.1 msec, respectively. Areas under the curve of native T1 relaxation times were higher in comparison with those of other cardiac MR parameters. The areas under the curve of native T1 relaxation times were 0.94 compared to 0.90 for late gadolinium enhancement, 0.79 for T2 ratio, 0.71 for extracellular volume fraction, and 0.63 for early gadolinium enhancement ratio.

Sensitivity was 92 percent, specificity was 91 percent and diagnostic accuracy was 91 percent for native T1 relaxation times. These numbers were equivalent when compared to those of the established Lake Louise criteria, for which sensitivity is 92 percent, specificity is 80 percent and diagnostic accuracy is 85 percent.

“In patients with contraindications for gadolinium-based contrast media, native myocardial T1 mapping may replace current Lake Louise criteria without sacrificing diagnostic accuracy,” wrote the study’s authors. Luetkens and colleagues suggest the need for further prospective studies to confirm their findings.