Prolonged fasting for optimizing myocardial fluorodeoxyglucose suppression

Background PET with 18 F-fluorodeoxyglucose ( 18 F-FDG) is widely used to evaluate inflammatory cardiac disorders such as sarcoidosis and myocarditis. However, physiologic myocardial uptake can obscure pathological uptake and must be suppressed. Objective To determine the effectiveness of fasting alone in suppressing physiological myocardial uptake and to establish a practical imaging protocol. Methods We retrospectively reviewed patients who underwent whole-body 18 F-FDG PET/CT for oncologic indications between January 2019 and December 2020. Patients were categorized by fasting duration: Group A (<12 h), Group B (12–17 h), and Group C (≥18 h). Two independent readers qualitatively graded myocardial FDG uptake, with adequate suppression defined as grade 0 (no uptake) or grade 1 (uptake ≤ liver background). Uptake above liver background (grade 2) was considered inadequate. Interreader agreement was assessed using Cohen’s Kappa. Results A total of 450 patients were included (150 per group). Adequate myocardial suppression was achieved in 77.3, 66, and 60% of patients in Groups C, B, and A, respectively ( P = 0.005). Suppression was not associated with blood glucose, age, or diabetes. However, significant associations were observed with gender ( P = 0.024) and BMI ( P = 0.006). Interreader agreement was almost perfect (Cohen’s Kappa 0.909; 95% CI: 0.868–0.950). Conclusion Fasting for ≥18 h is more effective than shorter durations in suppressing physiologic myocardial FDG uptake, enabling evaluation of myocardial inflammation. This simple and feasible protocol is particularly valuable in resource-limited settings. Visual grading demonstrated excellent reproducibility, supporting its role in clinical practice.