An optimal condition for the evaluation of human brown adipose tissue by infrared thermography

Brown adipose tissue (BAT) is responsible for non-shivering thermogenesis and is an attractive therapeutic target for combating obesity and related diseases. Human BAT activity has been evaluated by 18 F-fluorodeoxyglucose-positron emission tomography/computed tomography (18 FDG-PET/CT) under acute cold exposure, but the method has some serious limitations, including radiation exposure. Infrared thermography (IRT) may be a simple and less-invasive alternative to evaluate BAT activity. In the present study, to establish an optimal condition for IRT, using a thermal imaging camera, skin temperature was measured in the supraclavicular region close to BAT depots (T-scv) and the control chest region (T-c) in 24 young healthy volunteers. Their BAT activity was assessed as the maximal standardized uptake value (SUVmax) by (18)FDG-PET/CT. Under a warm condition at 24-27 degrees C, no significant correlation was found between the IRT parameters (T-scv, T-c,T-, and the difference between T-scv and T-c,T-, Delta temp) and SUVmax, but 30-120 min after cold exposure at 19 degrees C, T-scv and Delta temp were significantly correlated with SUVmax (r = 0.40-0.48 and r = 0.68-0.76) Delta temp after cold exposure was not affected by mean body temperature, body fatness, and skin blood flow. A lower correlation (r = 0.43) of Delta temp with SUVmax was also obtained when the participant's hands were immersed in water at 18 degrees C for 5 min. Receiver operating characteristic analysis revealed that Delta temp after 30-60 min cold exposure can be used as an index for BAT evaluation with 74% sensitivity, 92% specificity, and 79% diagnostic accuracy. Thus, IRT may be useful as a simple and less-invasive method for evaluating BAT, particularly for large-scale screening and longitudinal repeat studies.