BACKGROUND Obesity results from an imbalance between energy intake and expenditure. In rodents and newborn humans, brown adipose tissue helps regulate energy expenditure by thermogenesis mediated by the expression of uncoupling protein 1 (UCP1), but brown adipose tissue has been considered to have no physiologic relevance in adult humans. METHODS We analyzed 3640 consecutive 18F-fluorodeoxyglucose (18F-FDG) positron-emission tomographic and computed tomographic (PET–CT) scans performed for various diagnostic reasons in 1972 patients for the presence of substantial depots of putative brown adipose tissue. Such depots were defined as collections of tissue that were more than 4 mm in diameter, had the density of adipose tissue according to CT, and had maximal standardized uptake values of 18F-FDG of at least 2.0 g per milliliter, indicating high metabolic activity. Clinical indexes were recorded and compared with those of date-matched controls. Immunostaining for UCP1 was performed on biopsy specimens from the neck and supraclavicular regions in patients undergoing surgery. RESULTS Substantial depots of brown adipose tissue were identified by PET–CT in a region extending from the anterior neck to the thorax. Tissue from this region had UCP1-immunopositive, multilocular adipocytes indicating brown adipose tissue. Positive scans were seen in 76 of 1013 women (7.5%) and 30 of 959 men (3.1%), corresponding to a female:male ratio greater than 2:1 (P<0.001). Women also had a greater mass of brown adipose tissue and higher 18F-FDG uptake activity. The probability of the detection of brown adipose tissue was inversely correlated with years of age (P<0.001), outdoor temperature at the time of the scan (P= 0.02), beta-blocker use (P<0.001), and among older patients, body-mass index (P = 0.007). CONCLUSIONS Defined regions of functionally active brown adipose tissue are present in adult humans, are more frequent in women than in men, and may be quantified noninvasively with the use of 18F-FDG PET–CT. Most important, the amount of brown adipose tissue is inversely correlated with body-mass index, especially in older people, suggesting a potential role of brown adipose tissue in adult human metabolism.

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PET/CT imaging with 18 F-FDG has been used to detect inflammation in carotid and aortic plaque; its use in detecting coronary plaque has been limited by avid 18 F-FDG uptake by the myocardium. We investigated whether 18 F-FDG PET/CT could be used to image inflammation in coronary arteries as a potential noninvasive method to detect vulnerable plaque. Methods: We retrospectively studied 32 patients treated for malignancy who underwent 18 F-FDG PET/CT and concomitant cardiac catheterization. As part of the recently described protocol, all patients were instructed to eat a low-carbohydrate, high-fat meal the night before and drink a vegetable oil drink the morning of the study. We reviewed the patients' baseline characteristics and their 18 F-FDG PET/CT scans for adequacy of myocardial uptake suppression and correlated the presence of angiographically apparent plaque with 18 F-FDG uptake in the major coronary arteries. Two independent observers assessed the angiographic images and 18 F-FDG PET scans. Results: A total of 95% of patients had 2 or more coronary disease risk factors, and 25% had unstable symptoms; 30% of index catheterizations resulted in intervention. In 20 of 32 patients (63%), myocardial suppression was good (12) or adequate (8). Inadequate suppression was due to self-reported dietary nonadherence. Patients with good, adequate, and poor suppression had maximal myocardial standardized uptake values of 2.8 6 0.7, 5.0 6 1.3, and 17.0 6 9.7, respectively. We identified 18 F-FDG uptake in 15 patients in 1 or more coronary segments. A trend to significance in correlation between presence of angiographic disease and signal in the vessel was observed (P 5 0.07; 80 vessels examined). A total of 7 patients with significant coronary artery disease had aortic 18 F-FDG uptake. Conclusion: In this retrospective study, we demonstrated the potential use of 18 F-FDG PET in imaging of inflammation in coronary arteries. The potential of 18 F-FDG PET is also being investigated in a prospective study.

Disclosure StatementThis is not an industry supported study. Drs. Catcheside, Mercer, McEvoy, Lehman, Antic, and Thompson have indicated no financial conflicts of interest.