Incidence and characteristics of 18F-FDG uptake in brown adipose tissue induced by β3-adrenergic receptor agonist treatment in 18F-FDG PET/CT images in elderly patients over 50 years of age

Objective The incidence of 18F-fluorodeoxyglucose (FDG) uptake in brown adipose tissue (BAT) in elderly patients and the characteristics of 18F-FDG uptake in BAT induced by β3-adrenergic receptor (β3-AR) agonist treatment remain unclear. The purpose of this study was to clarify the incidence of radiotracer uptake during 18F-FDG positron emission tomography (PET)/computed tomography (CT) in patients over 50 years of age in daily clinical practice, and to explore the characteristics of 18F-FDG uptake in BAT induced by β3-AR agonist treatment. Methods We retrospectively reviewed the 18F-FDG-PET images of 29 patients over 50 years of age who showed 18F-FDG uptake in BAT. We analyzed the association between β3-AR agonist treatment and 18F-FDG uptake in BAT by focusing on the following 8 regions - the cervical, periclavicular, axillary, mediastinal, paraspinal, para-abdominal aortic, perirenal, and perisplenic regions. Results The results revealed a significant difference in the FDG uptake in the BAT of the perirenal region between patients who were under and not under β3-AR agonist treatment at the time of the PET examination. Comparison of the standardized uptake value maximum (SUVmax) also showed a significant difference in 18F-FDG uptake in the BAT of the perirenal region between patients who were under and not under β3-AR agonist treatment at the time of the PET examination (p = 0.001). Conclusion In patients over 50 years of age who show 18F-FDG uptake in BAT, increased 18F-FDG uptake due to the influence of β3-AR agonists should be considered. Presence of 18F-FDG uptake in the BAT of the perirenal region may serve as a clue to considering β3-AR agonist-induced uptake.