PET/CT > Artifacts & Pitfalls > Brown Fat

Brown Fat

Often a pattern of multi-focal intense symmetric uptake along the neck, supraclavicular regions, mediastinum, and paraspinal regions can be seen, especially in children. The PET/CT fusion images localize this uptake to areas of fat, rather than to any other soft tissues.

22-year-old female patient with history of large B-cell lymphoma status post 6 cycles of chemotherapy. PET/CT ordered for restaging. Symmetrical FDG activity is seen within brown fat in the neck and chest, a benign finding.

Brown fat activity on attenuation-corrected and non-attenuation-corrected PET data sets

Research has shown that it is specifically the brown adipocytes that take up FDG. Brown adipocytes become activated as one of the initial steps in thermogenesis in response to cold (i.e. "shivering"). Through sympathetic innervation, glycolysis in brown fat is significantly increased. Higher levels of circulating catecholamines in anxious patients may also play a role in the stimulation of brown fat FDG metabolism. Keeping the injection rooms at warmer temperatures may help in avoiding this problem. If confident interpretation cannot be made due to brown fat activity, premedication with a small dose of a benzodiazepine (e.g. Valium) can help prevent brown fat activity on a repeat study.