Intraindividual difference between supraclavicular and subcutaneous proton density fat fraction is associated with...

Brown adipose tissue (BAT) activity is triggered by cold exposure resulting in an increased resting energy expenditure, called cold-induced non-shivering thermogenesis (CIT). Magnetic resonance (MR)-based proton density fat fraction (PDFF) of the supraclavicular fossa has been proposed as a surrogate marker of human BAT. The present study investigates supraclavicular PDFF in relation to CIT.

For this prospective cross-sectional study 39 adults were recruited, from a cross-sectional study, exploring energy expenditure after cold exposure compared to thermoneutral conditions. Participants underwent additional MR examination of neck, pelvis, and abdomen. Supraclavicular and subcutaneous gluteal adipose tissue depots were segmented semi-automatically. Mean PDFF was assessed for each compartment and the delta PDFF was calculated as the difference of both. Correlation analysis of supraclavicular PDFF to CIT was performed for the whole cohort and subgroups, sorted by body mass index (BMI) and body fat percentage.

Median age of participants (61.5% female) was 27 years. BMI ranged from 19.0 to 38.5 kg/m², with body fat percentages from 4.6% to 45.3%. Median supraclavicular PDFF of 82.5% and median gluteal PDFF of 91.1%, were significantly different (P<0.0001). Median delta PDFF was 8.8% (3.9-21.9%). Mean CIT was 4.7%±9.0%. No statistically significant correlation of supraclavicular PDFF and CIT was found in the whole cohort and in most of the observed subgroups. Just the subgroup with normal body fat percentage revealed significant correlations between supraclavicular PDFF and CIT (rho =-0.59; P=0.003). Delta PDFF was significantly associated with CIT (rho =0.36; P=0.026).

PDFF is influenced by adiposity. Therefore, if supraclavicular PDFF is used as approach to indirectly assess BAT presence, body composition should be considered. Delta PDFF, as the difference between gluteal and supraclavicular PDFF, may be a marker of CIT.