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 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (18FDG-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 (Tscv) and the control chest region (Tc) in 24 young healthy volunteers. Their BAT activity was assessed as the maximal standardized uptake value (SUVmax) by 18FDG-PET/CT. Under a warm condition at 24-27°C, no significant correlation was found between the IRT parameters (Tscv, Tc,, and the difference between Tscv and Tc,, Δtemp) and SUVmax, but 30-120 min after cold exposure at 19°C, Tscv and Δtemp were significantly correlated with SUVmax (r = 0.40-0.48 and r = 0.68-0.76). Δtemp after cold exposure was not affected by mean body temperature, body fatness, and skin blood flow. A lower correlation (r = 0.43) of Δtemp with SUVmax was also obtained when the participant's hands were immersed in water at 18°C for 5 min. Receiver operating characteristic analysis revealed that Δtemp 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.