Quantifying Interscapular Brown Fat Activity

The temperature over interscapular BAT (iBAT) was measured for 10 consecutive days using a thermal camera (FLIR T-650sc, FLIR Systems, Wilsonville, OR, USA) after 4 h of fasting to avoid BAT activation after a meal. The researchers were “blinded” to the group of animals that was scanned since the estrous cycle was determined after the measurements were performed. The interscapular area of the animals was shaved the day before the experiment and additionally when necessary during the 10 days of the experiments. For measurements, each animal was placed in a clean polystyrene cage. Animals were allowed to adjust to new environment and filmed with thermal camera for 30 s. The camera software calculates the object’s temperature by taking into account the emissivity of mouse skin (e = 0.97), reflected room temperature (24.8 ± 0.8 °C), air temperature (24.2 ± 0.6 °C), relative humidity (60.2 ± 4.4%, n = 16), and distance to the object (1 m) as these values can affect the measurements. These values did not differ between the tested groups.
To determine BAT activity we calculated iBAT heat energy output in watts (W) with the Stefan-Boltzmann law (17 (link)):
where ϵ is emissivity of 0.97, σ is Stefan-Boltzmann’s constant (5.676 × 10⁻⁸ Wm² K⁴), A is an area of the skin warmer than 34.6 °C (region of interest) in m², and T is the mean temperature of the area in K.