Is FDG PET useful to evaluate brown fat?
Yes. FDG uptake in brown fat is seen in about 5% to 10% of patients and is most often seen symmetrically in the supraclavicular, mediastinal, paravertebral, posterior intercostal, and retroperitoneal paraaortic and perinephric locations. A specific diagnosis is made when corresponding CT or MR images demonstrate fat attenuation or signal intensity, respectively. Brown fat is responsible for heat production through nonshivering thermogenesis, and factors that predispose to brown fat activation include cold exposure, young age, female gender, low body mass index, a nondiabetic state, and use of sympathetic stimulants such as nicotine or ephedrine. The amount and metabolic activity of brown fat is inversely proportional to adiposity, so there is much interest in developing new ways of increasing brown fat in the body to combat obesity and metabolic syndrome.