Intraindividual difference between supraclavicular and subcutaneous proton density fat fraction is associated with cold-induced thermogenesis

Abstract

Background: 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.Methods: 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.Results: Median age of participants (61.5% female) was 27 years. BMI ranged from 19.0 to 38.5 kg/m 2 , 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).Conclusions: 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.

Automated segmentation of the human supraclavicular fat depot via deep neural network in water-fat separated magnetic resonance images

“…As shown in Figure 4, the detailed pre-processing includes following two steps: in the first step, voxel-wise masks are applied referring to PDFF maps (annotation regions satisfy PDFF >35% and PDFF <110%) and T 2 * maps (annotation regions satisfy T 2 * >10 ms). The PDFF threshold of 35% was chosen based on literature values (14,(16)(17)(18)(19)27,28) combined with empiric experience with our data. As bone exhibits much lower T 2 * values than fat, the additional T 2 * maps can help to distinguish fat from bone signal.…”

“…Chemical-shift based water-fat imaging techniques acquire gradient echoes at different echo times (TEs) to resolve the water-fat separation, rendering a proton density fat fraction (PDFF) map. Due to the clinical availability of this technique, it has become a popular tool in the research of BAT with MRI There is controversy about the correlation between the MRI-based fat fraction in a given region of interest (ROI) scanned during rest and the BAT presence measured with PET during BAT activation (12)(13)(14)(15). Yet, some MR-only studies revealed significant relative change of PDFF during BAT activation paradigms in comparison to baseline PDFF measurements (16)(17)(18)(19).…”

“…In addition to a lack of a consistent anatomical border definition for BAT studies, there is also a lack of consensus on the optimal PDFF threshold used for defining potential BAT regions. While it has been shown that PDFF in infants of the supraclavicular fossa can be as low as 17% (26), MR studies in adults have been using the threshold of PDFF as 30% (16)(17)(18)(19) or 50% (14,27,28) to exclude adjacent voxels originating from muscles or vessels after manual annotation. Being directly adjacent to bones like the scapula and the clavicle, the bone signal can be easily misinterpreted as BAT, as bone marrow exhibits similar values on the PDFF maps.…”