Imal fasting duration to effectively suppress physiological 18f fluorodeoxyglucose (fdg) myocardial uptake on a positron emission tomography scan.

Fatima Abdullahi Ali, Aga Khan University


Background: Positron emission tomography (PET) with 18F fluorodeoxyglucose (FDG) is used in evaluation of inflammatory disorders, including the heart such as cardiac sarcoidosis and myocarditis. However, the normal uptake of the myocardium is a challenge as it can obscure pathological uptake in these conditions. The primary objective of this study is to determine the optimal fasting duration to suppress physiological myocardial uptake and thereafter establish an imaging protocol.

Methods: Patients who had whole body FDG PET CT examination for oncological evaluation at the Aga Khan University Hospital between January 2019 and December 2020 were retrospectively reviewed. Patients were divided into three groups based on fasting duration: Group A = less than 12 hours, Group B = 12-17 hours and Group C = 18 hours and more. For qualitative assessment, two independent readers visually graded myocardial FDG uptake where adequate suppression was defined as no uptake (grade 0) or uptake similar or below liver background (grade 1) on visual analysis.

Results: A total of 450 patients were included in the study with each fasting duration group containing 150 patients. There was association between duration of fasting and myocardial FDG uptake suppression with 77.3%, 66% and 60% of patients achieving adequate myocardial FDG suppression in Group C, Group B and Group A respectively (P=0.005). There was no significant association between the myocardial uptake pattern and blood glucose level, age and diabetes. However, there was statistically significant association between the myocardial uptake suppression with gender and body mass index (BMI). There was almost perfect inter-reader agreement on visual grading of myocardial FDG uptake.

Conclusion: Fasting for 18 hours or more is the optimal fasting duration to suppress myocardial uptake to allow for evaluation of myocardial inflammation on FDG PET and provides a practical and easy v to implement imaging protocol. Visual grading of myocardial FDG uptake has almost perfect inter-observer agreement which supports the reproducibility of qualitative analysis method. Recommendations: For patients evaluated with FDG PET/CT scan for inflammatory cardiac indications, fasting at least 18 hours is recommended for adequate myocardial uptake suppression. Visual grading of myocardial uptake has high reproducibility and can be a suitable method for routine clinical application in patients undergoing FDG PET for assessment of myocardial inflammation. A larger prospective multi-institutional study comparing different protocols in the literature to establish the optimal method of suppressing normal myocardial FDG uptake is needed.