1316061 - Feasibility of T1rho measurements in patients with Single Ventricle Disease

Single Ventricle Disease (SVD) is an umbrella term for several congenital heart diseases which occur when a child is born with effectively only one functioning ventricle. SVD is repaired surgically, culminating in the Fontan procedure, which connects the vena cavae directly to the pulmonary circulation so that the single ventricle pumps exclusively to the systemic circulation. While the Fontan procedure greatly improves survival in SVD patients, it also leads to altered physiology resulting in multiple adverse effects such as hepatic and cardiac fibrosis. However, the timing and pathogenesis of these effects are still poorly understood. Because these patients are young and prone to hemodynamic instability, it is important that they be monitored without radiation and non-invasively whenever possible. T1⍴ relaxation time is an endogenous magnetic resonance contrast mechanism that utilizes a spin-lock pulse to suppress low frequency background contributions to relaxation that obscure image contrast between normal and fibrotic tissue. However, T1r has not yet been studied in SVD. Thus, we sought to assess the feasibility of T1⍴ mapping to characterize hearts and livers in patients with SVD.

Methods:

20 SVD patients underwent cardiovascular magnetic resonance scanning in a Siemens 1.5 T Avanto FIT scanner with electrocardiogram gating prior to Fontan procedure. 2D T1r sequences were performed at apical, mid-ventricular, and basal slice positions using a motion- and heart rate-corrected spin echo, spin lock pulse cluster at end-systole, consisting of 8 spin lock times. The resulting data were used to estimate relaxation rate R1r (1/T1r) and generate T1r maps for each slice location in each patient. Cardiac T1r maps were analyzed by semi-automatic contouring of the myocardium in cvi42. Liver T1r maps were processed and analyzed in pMRI using the mean of five circular regions-of-interest in the parenchyma of the liver, avoiding major vessels. Statistical analysis was performed in R.

Results:

Representative T1r maps are shown in Figure 1. Median [IQR] T1r was 90 [83, 102] ms, 79 [76, 84] ms, and 79 [73, 84] ms for apical, mid-ventricular, and basal short-axis cardiac slices, respectively (Figure 2). Median liver T1r was 37 [35, 40] ms. T1r varied significantly by location (p< 1e-8); liver T1r was significantly lower than cardiac T1r for every slice location (p< 1e-4 for all), while cardiac T1r did not differ by slice location.

Conclusion:

These preliminary results demonstrate the feasibility of performing T1 imaging in pediatric patients with SVD. Cardiac T1r in these patients was higher than values reported in the literature for healthy adult patients (65.4 ± 5.24 ms).¹ Future studies will focus on larger cohorts (including controls), different timepoints after Fontan procedure, and correlation of T1r with other measurements of fibrosis to elucidate the mechanisms underlying adverse outcomes in SVD patients.