Cold-Activated Brown Adipose Tissue in Healthy Men
Figure 1. Brown-Adipose-Tissue Activity as Assessed by PET–CT with 18F-FDG.
The results of PET–CT scanning in 9 of 24 subjects show variable physiologic uptake and distribution of 18Ffluorodeoxyglucose (18FFDG) in adipose tissue (Panel A). The images in the top row are from lean subjects with the highest levels of brownadiposetissue activity (>500 kBq), images in the middle row are from lean subjects with median levels of activity, and images in the bottom row are from obese or overweight subjects with the lowest levels of activity (<100 kBq). The supraclavicular region has the greatest amount of brown adipose tissue. A PET scan in the transverse plane (Panel B) shows the areas of brown adipose tissue (e.g., arrow), and a CT scan (Panel C) con firms the areas of brown adipose tissue (arrow) according to fat density and location. Fusion of the PET and CT scans (Panel D) shows that 18FFDG uptake is localized in fatty tissue (arrow). Comparative PET–CT scans (Panel E) reveal the patterns of 18FFDG uptake in the same subject from the lean group after exposure to cold and under thermoneutral conditions.
Twenty-three of the 24 subjects had definite, al- beit highly variable, amounts of 18F-FDG activity in the neck, supraclavicular region, chest, and ab- domen (Fig. 1A). On the fused PET–CT images, the activity was located not in muscle tissue but in fat tissue, which was therefore considered to
be brown adipose tissue (Fig. 1B through 1D). All lean subjects and 13 of the 14 overweight or obese subjects had evidence of brown-adipose- tissue activity in response to cold exposure. Mean brown-adipose-tissue activity was significantly lower in the overweight or obese subjects (102±93 kBq) than in the lean subjects (428±394 kBq) (P=0.007) (Table 2). The volume of brown adipose
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