The right ventricle in congenital heart disease - Cardiac T1 mapping for measurements of diffuse myocardial fibrosis
© Al-Wakeel et al. 2016
Published: 27 January 2016
Measurements of myocardial extracellular volume (ECV) through cardiac magnetic resonance (CMR) based T1 mapping allow for non-invasive quantification of diffuse myocardial fibrosis. The evaluation of the right ventricle (RV), often mainly affected in congenital heart disease (CHD), is complicated by its typical morphologic characteristics - a thin myocardium and a distinct trabeculation. This study aims to evaluate ECV measurements of the RV in patients with CHD and to introduce a tool that simplifies RV ECV analysis.
CHD patients (n = 47; mean age 27.9 ± 9.6 years) were prospectively enrolled and compared with 17 healthy volunteers (mean age 25.1 ± 2.7 years). T1 maps were generated with Modified Look-Locker Inversion recovery (MOLLI) T1 mapping in a single midventricular plane in short axis (SAX) and transverse orientation (TRANS) before and 15 minutes after bolus application of Gd-DOTA or Gd-DTPA. To measure ECV, T1 values of the anterior or inferior RV wall were used. Regions of interest (ROIs) were evaluated with regard to image quality (1: no artifacts in RV, good contrast between blood and myocardium; 2: minor artifacts, good/sufficient contrast; 3: major artifacts and/or insufficient contrast) and ROI thickness (1: > 2 pixels; 2: 1-2 pixels; 3: < 1 pixel). ECV from plane RV ROIs were compared with ECV obtained from a custom-made tool that derives the mean T1 values from a curved line manually drawn in the center of the myocardial wall ("centerline ECV").
RV ECV could be determined in 40 patients (32 ± 0.05) and 9 volunteers (0.28 ± 0.03) with a strong correlation of ECV values from SAX and TRANS (r = 0.91, and 0.95; p < 0.05, respectively). In both groups average image quality was rated with grade 1 and mean RV ROI thickness with grade 2. ECV could not be measured in cases of insufficient contrast between blood and myocardium or ROI thickness < 1 pixel. ECV from ROIs and corresponding centerline ECV correlated strongly in SAX and TRANS in CHD patients (r = 0.97, and 0.92; p < 0.05, respectively) and volunteers (r = 0.91; p < 0.05, respectively).
1. RV ECV can be assessed with T1 mapping in SAX and TRANS provided that
a) image quality allows for sufficient distinction between blood and myocardium, and
b) RV wall thickness is > 1 pixel.
2. The application of a simple line centered in the RV myocardium instead of a plane ROI simplifies and accelerates measurements of RV ECV.
Under these conditions, measurements of RV ECV can be integrated into clinical CMR routine across a wide spectrum of CHD.
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