Assessment of sympathetic reinnervation after cardiac transplantation using hybrid cardiac PET/MRI: A pilot study

Background Sympathetic reinnervation after heart transplantation (HTX) is a known phenomenon, which has an impact on patient heart rate variability and exercise capacity. The impact of reinnervation on myocardial structure has not been evaluated yet. Propose To evaluate the feasibility of simultaneous imaging of cardiac reinnervation and cardiac structure using a hybrid PET/MRI system. Study type Prospective / pilot study. Subjects Ten patients, 4-21 years after cardiac transplantation. Field Strength/Sequence 3 T hybrid PET/MRI system. Cine SSFP, T-1 mapping (modified Look-Locker inversion recovery sequence) pre/postcontrast as well as dynamic [C-11]meta-hydroxyephedrine ([C-11]mHED) PET. Assessment All MRI and PET parameters were evaluated by experienced readers using dedicated postprocessing software packages for cardiac MRI and PET. For all parameters a 16-segment model for the left ventricle was applied. Statistical Tests Mann-Whitney U-test; Spearman correlations. Results Thirty-six of 160 myocardial segments showed evidence of reinnervation by PET. On a segment-based analysis, mean native T-1 relaxation times were nonsignificantly altered in segments with evidence of reinnervation (1305 +/- 151 msec vs. 1270 +/- 112 msec; P = 0.1), whereas mean extracellular volume (ECV) was significantly higher in segments with evidence of reinnervation (35.8 +/- 11% vs. 30.9 +/- 7%; P = 0.019). There were no significant differences in wall motion (WM) and wall thickening (WT) between segments with or without reinnervation (mean WM: 7.6 +/- 4 mm vs. group B: 9.3 +/- 7 mm [P = 0.13]; WT: 79 +/- 63% vs. 94 +/- 74% [P = 0.27]) under resting conditions. Data Conclusion The assessment of cardiac reinnervation using a hybrid PET/MRI system is feasible. Segments with evidence of reinnervation by PET showed nonsignificantly higher T-1 relaxation times and a significantly higher ECV, suggesting a higher percentage of diffuse fibrosis in these segments, without impairment of rest WM and WT. Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;50:1326-1335.