PET-CT is the standard method for detecting brown adipose tissue (BAT) in humans. Alternatives are required because of the radiation and cost of PET-CT imaging. We reported in a pilot study of 29 scans that infrared thermography (IRT) showed promise as a tool for detecting BAT1.
To evaluate the value of IRT in detecting BAT status and changes in BAT activity.
Eighty-four PET-CT scans were evaluated after 3hr of cooling at 19°C, in parallel with skin temperature measurements overlying the supraclavicular (SCL) fossa and the lateral mediastinum (control). BAT-positivity was defined by SUV≥2 on PET-CT. A subgroup of 12 subjects participated in a placebo-controlled study of the effect of glucocorticoids on BAT.
Forty out of the 84 scans were BAT positive. Compared to the BAT-negative group, left SCL temperature was higher in the BAT-positive group before (32.8 vs 33.3°C; p=0.03) and throughout cooling (p<0.001). The control temperature or temperature difference (Δtemp) between left SCL and control area did not differ significantly between the groups. Left SCL and control temperatures fell significantly (p<0.001) with left SCL temperature being higher (p=0.003) than control temperature throughout cooling. On ROC analysis, the left SCL temperature or ∆temp conferred a sensitivity of 20% at a specificity of 90% for BAT detection. The findings were similar on the right. Glucocorticoids reduced BAT activity significantly (SUVmax 6.1±2.2 to 3.7±1.2,
p<0.05). Left SCL temperature fell by a significantly greater degree (p<0.05) during glucocorticoid treatment after cooling (-0.3±0.1 vs -0.7±0.10C).
SCL temperatures are higher in BAT-positive than BAT-negative subjects but poorly discriminate between BAT-positive and -negative subjects. Within subjects, a fall in BAT activity is accompanied by a fall in SCL temperatures.
Conclusion: IRT is an unreliable tool for detecting BAT. It may have a role for monitoring changes in BAT activity within individuals.