Near-Infrared Spatially Resolved Spectroscopy as an Indirect Technique to Assess Brown Adipose Tissue in Young Women

Purpose: Near-infrared spectroscopy (NIRS) has recently been proposed as an indirect technique to assess brown adipose tissue (BAT) in young men. NIRS arises as a novel technique to avoid the limitations of the "gold-standard" 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]DG) positron emission tomography combined with X-ray computed tomography (PET/CT). The aim of this study was to examine the association between near-infrared spatially resolved spectroscopy (NIR_SRS) parameters and BAT volume and activity estimated by [¹⁸F]DG-PET/CT in 18 young healthy women.

Procedures: NIR_SRS parameters [tissue saturation index and concentrations of total haemoglobin, oxy-haemoglobin, and deoxy-haemoglobin] were continuously measured in the supraclavicular and forearm regions, in both warm and cold (2 h of personalised cold exposure) conditions. Then, the NIR_SRS data were analysed as an average of 5 min in 4 different periods: (i) warm period as the baseline record, (ii) cold period I, (iii) cold period II, and (iv) cold period III. The data were then correlated with BAT volume and activity (SUV_mean and SUV_peak) estimated by [¹⁸F]DG-PET/CT.

Results: There was no association between the NIR_SRS parameters in the supraclavicular region in warm conditions (no previous cold exposure) and BAT volume and activity (P > 0.05). Similarly, the cold-induced changes of the NIR_SRS parameters in the supraclavicular region were not associated with BAT volume and activity (P > 0.05).

Conclusions: NIR_SRS does not seem to be a valid technique to indirectly assess BAT in young healthy women. Further research is needed to validate this technique against other methods such as PET/CT using different radiotracers or magnetic resonance imaging.