Brown Fat Imaging with 18F-6-Fluorodopamine PET/CT, 18F-FDG PET/CT, and 123I-MIBG SPECT: A Study of Patients Being Evaluated

Several radiopharmaceuticals such as 18F-FDG, 123I-metaiodo-benzylguanidine (MIBG), and 99mTc-tetrofosmin have demon-strated uptake in brown adipose tissue (BAT). It is important to recognize these normal variants so that they are not mis-interpreted as a significant pathologic state. In addition, these radiopharmaceuticals may shed light on BAT physiology. 18F-6-fluorodopamine (F-DA) is being used as a PET radiophar-maceutical to imageadrenergic innervation andsuspectedpheo-chromocytoma. Past reports have suggested that BAT is increased in pheochromocytoma patients. Methods: The im-ages of 96 patients evaluated with 18F-F-DA or 18F-FDG PET/ CT for known or suspected pheochromocytoma were reviewed retrospectively to determine whether localized uptake of a pat-tern typically associated with BAT was present. When available, contemporaneous images obtained using 123I-MIBG were also reviewed for the presence of BAT. Results: Of 67 patients im-aged with 18F-F-DA, BAT was found in 17.9%. Of 83 patients im-aged with 18F-FDG, 19.2 % had BAT. Discordant findings related to uptake in BAT were often seen in patients studied with 18F-FDG, 18F-F-DA, or 123I-MIBG. Overall, 26 (27.0%) of 96 pa-tients showedBAT on at least 1 of the 3 imagingmodalities.Con-clusion: 18F-F-DA can image BAT, most likely by localizing to sympathetic innervations in a manner similar to 123I-MIBG. Pa-tients with pheochromocytoma may have a greater BAT tissue mass or activation because of elevated levels of circulating cat-echolamines. Quantitative PET with 18F-FDG and 18F-F-DA may have a role in in vivo studies of BAT physiology in humans or an-imal models