Murine brown fat metabolism measured by infrared thermography correlates with PET FDG uptake

Objectives Brown adipose tissue (BAT) has important thermoregulatory function. BAT exhibits thermogenesis in response to cold via extremely high glycolytic metabolism. BAT metabolism is highly dynamic, changing within minutes. The rapid changes of BAT metabolism are difficult to measure via traditional FDG PET. Infrared (IR) thermography is a promising alternative because the faster temporal response that should be able to capture the minute-to-minute dynamics of BAT metabolism that escape PET. To validate IR thermography, we hypothesized that the FDG PET signal will correlate with infrared (IR) thermography signal.

Methods Mice (n=15) were acclimated for at various temperatures (21°C - 31°C) to generate a spectrum of BAT activity. 35 µCi FDG was administered IP and allowed 1 hour of conscious uptake. IR images were acquired with a calibrated thermal camera (FLIR T420). The mice were subsequently anesthetized and PET scanned in a Genisys. BAT metabolism was measured by the ratio of IR signal to a control region and FDG uptake by a whole body activity ratio. We analyzed the IR and FDG PET relationship by regression modeling with D’Agostino-Pearson normality and goodness-of-fit tests.

Results At these physiology relevant tested conditions, the relationship of IR thermography and FDG PET based measurements of BAT activity are best described by an exponential fit: R2 = 0.71, p = 0.001.

Conclusions This correlation shows IR thermography is a powerful adjunct to PET for measuring BAT metabolism. IR thermography is a valuable and affordable tool that measures the BAT activity in real-time with, high sampling frequency and without perturbing the highly dynamic physiology of BAT. Moreover, we demonstrate that changes in the IR thermography signal precede the changes in the FDG uptake during mild BAT activation. With additional validation of IR thermography measurements of BAT activity, IR thermography can be an accurate, non-invasive, quantitative tool for measuring BAT activation.