Long fasting is effective in inhibiting physiological myocardial (18)F-FDG uptake and for evaluating active lesions of cardiac sarcoidosis

BACKGROUND: F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a promising modality for detecting active lesions of cardiac sarcoidosis (CS). However, determining whether (18)F-FDG uptake in the myocardium is physiological is challenging due to metabolic shift in myocardial cells. Although methods for inhibiting physiological myocardial (18)F-FDG uptake have been proposed, no standard methods exist. This study therefore aimed to compare the effect of an 18-h fast (long fasting (LF)) with heparin loading plus a 12-h fast (HEP) before (18)F-FDG PET scan. METHODS: We analyzed the effects of LF and HEP on the inhibition of physiological myocardial (18)F-FDG uptake in healthy subjects (18 in HEP and 19 in LF) and in patients with known or suspected CS (96 in HEP and 69 in LF). In CS, the lower uptake of (18)F-FDG in the myocardium was evaluated. A visual four-point scale was used to assess myocardial (18)F-FDG uptake in comparison with hepatic uptake (1 lower, 2 similar, 3 somewhat higher, 4 noticeably higher). RESULTS: Myocardial (18)F-FDG uptake was 1.68 ± 1.06 in LF and 3.17 ± 1.16 in HEP in healthy subjects (p < 0.0001), whereas it was 1.48 ± 0.99 in LF and 2.48 ± 1.33 in HEP in CS patients (p < 0.0001). Logistic regression and regression trees revealed the LF was the most effective in inhibiting myocardial (18)F-FDG uptake. In addition, serum free fatty acid levels on intravenous (18)F-FDG injection were a possible biomarker. CONCLUSIONS: LF is effective in inhibiting myocardial (18)F-FDG uptake, and consequently, it could be useful for evaluating active lesions of CS in (18)F-FDG PET images.