Detection of myocarditis using T1 and ECV mapping is not improved by early compared to late post-contrast imaging.

BACKGROUND: Cardiovascular magnetic resonance (CMR) of myocarditis may include early gadolinium enhancement (EGE) and global relative enhancement (GRE) by T1 -weighted images acquired before and early after contrast administration. However, the importance of timing for post-contrast imaging has not been evaluated using T1 mapping. We aimed to improve the understanding of the contrast mechanisms by evaluating whether early or late post-contrast T1 mapping was better at detecting myocarditis. METHODS: Controls and patients referred to evaluate myocarditis underwent 1·5T CMR. T1 mapping was performed before, and 3 min (early) and 21 min (late) after intravenous contrast (0·2 mmol kg-1 ). Extracellular volume fraction (ECV) and the GRE and EGE equivalents by T1 mapping were calculated. Focally affected myocardium in myocarditis was defined as increased native T1 compared to remote myocardium. RESULTS: The GRE equivalent by T1 mapping was higher in myocarditis (n = 19) compared to controls (n = 19) both early (P<0·001) and late (P<0·001). While remote myocardium in myocarditis had higher enhancement relative to skeletal muscle compared to controls early (P = 0·002) and late (P<0·001), ECV of skeletal muscle was lower compared to controls both early (P = 0·03) and late (P = 0·004), and remote myocardial ECV did not differ from controls early (P = 0·37) or late (P = 0·52). The difference in ECV between affected and remote myocardium was higher late compared to early by 5·3 ± 0·7 versus 4·0 ± 0·6%-points (P = 0·002). CONCLUSION: Quantitative evaluation by T1 mapping shows that early post-contrast imaging does not improve the detection of myocarditis compared to late post-contrast imaging. Focal myocardial abnormalities were more conspicuous late post-contrast.