Thermal Imaging Is a Noninvasive Alternative to PET/CT for Measurement of Brown Adipose Tissue Activity in Humans

Abstract

Obesity and its metabolic consequences are a major cause of morbidity and mortality. Brown adipose tissue (BAT) utilizes glucose and free fatty acids to produce heat, thereby increasing energy expenditure. Effective evaluation of human BAT stimulators is constrained by the current standard method of assessing BAT—PET/CT—as it requires exposure to high doses of ionizing radiation. Infrared thermography (IRT) is a potential noninvasive, safe alternative, although direct corroboration with PET/CT has not been established. Methods: IRT and 18F-FDG PET/CT data from 8 healthy men subjected to water-jacket cooling were directly compared. Thermal images were geometrically transformed to overlay PET/CT-derived maximum intensity projection (MIP) images from each subject, and the areas with the most intense temperature and glucose uptake within the supraclavicular regions were compared. Relationships between supraclavicular temperatures (TSCR) from IRT and the metabolic rate of glucose uptake (MR(gluc)) from PET/CT were determined. Results: Glucose uptake on MR(gluc)MIP was found to correlate positively with a change in TSCR relative to a reference region (r2 = 0.721; P = 0.008). Spatial overlap between areas of maximal MR(gluc)MIP and maximal TSCR was 29.5% ± 5.1%. Prolonged cooling, for 60 min, was associated with a further TSCR rise, compared with cooling for 10 min. Conclusion: The supraclavicular hotspot identified on IRT closely corresponded to the area of maximal uptake on PET/CT-derived MR(gluc)MIP images. Greater increases in relative TSCR were associated with raised glucose uptake. IRT should now be considered a suitable method for measuring BAT activation, especially in populations for whom PET/CT is not feasible, practical, or repeatable.

Evidence of high 18F‐fluorodeoxyglucose uptake in the subcutaneous adipose tissue of the dorsocervical area in young adults

“…We took pictures with an infrared thermograph (FLIRb60 Systems Australia Pty Ltd, Melbourne, Vic., Australia) before and after personalized cold exposure in a separate sample of 11 adults (n = 9 women, age 22.3 ± 1.4 years and body mass index 23.1 ± 3.0 kg m −2 ; n = 2 men, age 22.8 ± 4.2 years and body mass index 26.8 ± 11.1 kg m −2 ) in order to study the skin temperature of the dorsocervical and supraclavicular areas (Law et al, 2018). We placed the participants in a thermoneutral room, without a T-shirt, for 5 min before performing the three infrared pictures.…”

Brown Adipose Tissue: Multimodality Evaluation by PET, MRI, Infrared Thermography, and Whole‐Body Calorimetry (TACTICAL‐II)

“…Activated BAT raises the anterior supraclavicular temperature (Tscv), which is detectable by IRT. Tscv, measured by IRT, is correlated to maximal glucose uptake on PET‐CT images . MRI can measure fat fraction (FF ‐ defined as the proportion of the acquired signal derived from fat protons) and , which differ between BAT and WAT because of the former’s high intracellular and extracellular water content and because of differences in vasculature and mitochondria .…”

Infrared Thermography for Estimating Supraclavicular Skin Temperature and BAT Activity in Humans: A Systematic Review

“…The first study to use IRT to estimate SST was performed in 2011 . Ten studies were then published between 2011 and 2016 , six in 2017 , six in 2018 , and one until April 2019 .…”

“…Cold exposure is the main activator of BAT in humans . Most, but not all, of the identified studies ( n = 18; 75%) included cooling protocols, although the duration, temperature, and the way of inducing cooling differed between studies (Figure ). Nine out of these eighteen studies used hands/feet immersion in cold water (temperature 10.8°C ± 8.7°C, duration: 6.1 ± 6.8 minutes) .…”

“…Moreover, Thuzar et al performed two independent studies in which they compared IRT‐measured SST against BAT 18 F‐FDG uptake as measured by a PET/CT scan on the same day, reporting a positive and significant association between them. In contrast, Law et al made the same kind of measurements on separate days and using different cold exposure times. Comparing the latter two studies is, therefore, not easy.…”