Brown fat imaging with 18F6-fluorodopamine PET/CT, 18F-FDG PET/CT, and 123I-MIBG SPECT a study of patients being evaluated for pheochromocytoma

Several radiopharmaceuticals such as F-18-FDG, I-123-metaiodobenzylguanidine (MIBG), and Tc-99m-tetrofosmin have demonstrated uptake in brown adipose tissue (BAT). It is important to recognize these normal variants so that they are not misinterpreted as a significant pathologic state. In addition, these radiopharmaceuticals may shed light on BAT physiology. F-18-6-fluorodopamine (F-DA) is being used as a PET radiopharmaceutical to image adrenergic innervation and suspected pheochromocytoma. Past reports have suggested that BAT is increased in pheochromocytoma patients. Methods: The images of 96 patients evaluated with F-18-F-DA or F-18-FDG PET/ CT for known or suspected pheochromocytoma were reviewed retrospectively to determine whether localized uptake of a pattern typically associated with BAT was present. When available, contemporaneous images obtained using I-123-MIBG were also reviewed for the presence of BAT. Results: Of 67 patients imaged with F-18-F-DA, BAT was found in 17.9%. Of 83 patients imaged with F-18-FDG, 19.2% had BAT. Discordant findings related to uptake in BAT were often seen in patients studied with F-18-FDG, F-18-F-DA, or I-123-MIBG. Overall, 26 (27.0%) of 96 patients showed BAT on at least 1 of the 3 imaging modalities. Conclusion: F-18-F-DA can image BAT, most likely by localizing to sympathetic innervations in a manner similar to I-123-MIBG. Patients with pheochromocytoma may have a greater BAT tissue mass or activation because of elevated levels of circulating catecholamines. Quantitative PET with F-18-FDG and F-18-F-DA may have a role in in vivo studies of BAT physiology in humans or animal models.