Brown adipose tissue (BAT) is detectable by PET-CT using 18F-fluorodeoxyglucose. Alternative methods for studying BAT are needed because of the radiation and cost associated with PET-CT imaging. We aimed to assess the efficacy of infrared thermography (IRT) for detecting BAT as benchmarked to PET-CT imaging in 16 healthy volunteers (9M/7F, 36 ± 3.1 years, BMI 25.3 ± 1.6 kg/m²). Using IRT (B425 FLIR Systems), we measured the temperature of the skin overlying the supraclavicular fossa (SCV), where BAT is most commonly found in adults, and the mediastinum (MED), a region devoid of BAT, which serves as a BAT-negative control area. A positive PET-CT scan for BAT was defined as SUVmax > 1.5 in areas localising to fat attenuation on CT.
Among a total of 29 PET-CT scans, 15 were positive for BAT. The CVs of temperature overlying the SCV and MED from 16 subjects was <0.001%. The temperature in the SCV fossa was significantly higher than in the MED in both BAT Positive (32.3 ± 0.3 vs 30.0 ± 0.3 ^oC P <0.001) and BAT Negative groups (31.9 ± 0.5 vs 31.1 ± 0.5 ^oC, P =0.004). The mean temperature difference (Δtemp) between SCV and MED was greater in those with a positive scan (2.2 ± 0.3 vs 0.8 ± 0.2 ^oC, P=0.001). In a subgroup of 9 participants who underwent cold stimulation for 2 hours prior to imaging, Δtemp increased with cooling in the BAT positive group only. A temperature difference of 1˚C between the SCV and MED had a positive predictive value of 76.5% for BAT. In summary, IRT detected a temperature difference between the supraclavicular fossa and mediastinum that is significantly and consistently greater in PET positive subjects. This is the first study investigating the utility of IRT for detecting BAT benchmarked to PET-CT. IRT is a promising, non-invasive and convenient technique with good reproducibility that may complement PET-CT imaging in the study of BAT.

Supported by the NHMRC of Australia