Factors influencing brown fat activation in FDG PET/CT: a retrospective analysis of 15,000+cases

Objective: Brown fat can exhibit high uptake of fluorine-18 fludeoxyglucose (F-18-FDG) on positron emission tomography (PET) and interferes with interpretation of the scan. The goal of this study was to identify factors that may influence brown adipose tissue (BAT) activation. Methods: A retrospective study of 18F-FDG PET scans was performed using a database of 15,109 PET/CT reports. BAT activation reported by nuclear medicine physicians and factors influencing BAT activation were gathered. The data were analyzed using in-house software. Results: The total reported BAT activation was 3.6%. BAT activation was reported significantly more often in kpatients who were female (p < 0.0001), younger (p < 0.0001), with lower body mass index (p < 0.0001), with lower blood glucose levels (p = 0.01), indicated for breast cancer (p = 0.004), not administered chemotherapy recently before the scan (p < 0.0001) and shown to have BAT activation in a previous scan (p, 0.0001). BAT activation was also reported significantly more for lower outdoor temperatures (p, 0.0001) and for late morning scans than for afternoon (p = 0.005) and early morning (p = 0.001) scans. Conclusion: This retrospective study of 15,109 scans highlights multiple factors contributing to BAT activation on 18F-FDG PET. The identification of new factors influencing BAT and confirmation of previously identified factors with a larger data set can be used to more accurately identify patients at risk for BAT activation so that prevention strategies can be implemented.