A pilot study of 18F-FSPG SiPM-based PET/CT in patients referred for exclusion of active cardiac sarcoidosis and negative or non-diagnostic 18F-FDG PET/CT

1605 Objectives: 18F-FDG PET is currently used for the assessment of active cardiac sarcoidosis; however, up to 1/3 of patients fail to follow the required complex dietary restrictions, resulting in non-diagnostic scans. 18F-labeled FSPG, an L-glutamate derivative, is a promising radiotracer for PET imaging of the aminoacid antiporter system xC- that is involved in detoxification processes and balancing oxidative stress, including in sarcoidosis. No dietary restrictions are required prior to 18F-FSPG PET. This prospective pilot study evaluates the utility of 18F-FSPG PET for assessment of cardiac sarcoidosis, in comparison to negative or non-diagnostic 18F-FDG PET. Materials and Methods: Patients referred to Nuclear Medicine to rule out active cardiac sarcoidosis were prospectively enrolled after the 18F-FDG PET/CT results were negative or non-diagnostic. 18F-FSPG whole-body imaging started 46-67 minutes (mean±SD: 53.8±6.0), while dedicated cardiac imaging started 55-77 minutes (mean±SD: 65.9±5.9) after injection of 7.1-8.9 mCi (mean±SD: 8.1±0.5). The mean delay time between 18F-FDG PET and 18F-FSPG PET was 23.3 days. A state-of-the art SiPM-based PET/CT scanner was used. Results: Data from 3 women and 10 men, 32-79 year-old (mean±SD: 58.2±12.9) were collected. Six of the participants had no 18F-FDG uptake compatible with cardiac sarcoidosis; 2 of the 6 had 18F-FDG uptake in lung nodules and mediastinal lymph nodes, while 1 of the 6 had 18F-FDG uptake in mediastinal lymph nodes compatible with sarcoidosis. 18F-FSPG uptake was seen in the lung nodules and mediastinal lymph nodes in the same 3 participants with 18F-FDG uptake, while no 18F-FSPG uptake was identified in the myocardium. The remaining 7 patients had non-diagnostic cardiac 18F-FDG PET due to non-compliance with dietary instructions; 18F-FDG uptake in lung nodules and mediastinal lymph nodes was seen in 1 of these 7 patients. These lung nodules and mediastinal lymph nodes also had 18F-FSPG uptake. No 18F-FSPG myocardial uptake was identified in the 7 patients with non-diagnostic cardiac 18F-FDG PET. Conclusions: 18F-FSPG appears to show promising results in ruling out cardiac sarcoid involvement in a cohort with negative or non-diagnostic 18F-FDG PET. Further evaluation in larger cohorts is needed to confirm our data. In addition, future studies should evaluate 18F-FSPG usage in patients with confirmed active cardiac sarcoidosis.