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

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.

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.

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).

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.