Magnetic Resonance Imaging Cooling-Reheating Protocol Indicates Decreased Fat Fraction via Lipid Consumption in Suspected Brown Adipose Tissue

Abstract

ObjectivesTo evaluate whether a water-fat magnetic resonance imaging (MRI) cooling-reheating protocol could be used to detect changes in lipid content and perfusion in the main human brown adipose tissue (BAT) depot after a three-hour long mild cold exposure.Materials and MethodsNine volunteers were investigated with chemical-shift-encoded water-fat MRI at baseline, after a three-hour long cold exposure and after subsequent short reheating. Changes in fat fraction (FF) and R2*, related to ambient temperature, were quantified within cervical-supraclavicular adipose tissue (considered as suspected BAT, denoted sBAT) after semi-automatic segmentation. In addition, FF and R2* were quantified fully automatically in subcutaneous adipose tissue (not considered as suspected BAT, denoted SAT) for comparison. By assuming different time scales for the regulation of lipid turnover and perfusion in BAT, the changes were determined as resulting from either altered absolute fat content (lipid-related) or altered absolute water content (perfusion-related).ResultssBAT-FF decreased after cold exposure (mean change in percentage points = -1.94 pp, P = 0.021) whereas no change was observed in SAT-FF (mean = 0.23 pp, P = 0.314). sBAT-R2* tended to increase (mean = 0.65 s-1, P = 0.051) and SAT-R2* increased (mean = 0.40 s-1, P = 0.038) after cold exposure. sBAT-FF remained decreased after reheating (mean = -1.92 pp, P = 0.008, compared to baseline) whereas SAT-FF decreased (mean = -0.79 pp, P = 0.008, compared to after cold exposure).ConclusionsThe sustained low sBAT-FF after reheating suggests lipid consumption, rather than altered perfusion, as the main cause to the decreased sBAT-FF. The results obtained demonstrate the use of the cooling-reheating protocol for detecting changes in the cervical-supraclavicular fat depot, being the main human brown adipose tissue depot, in terms of lipid content and perfusion.

Characterizing active and inactive brown adipose tissue in adult humans using PET-CT and MR imaging

“…For example, an increase in blood flow or the consumption of fatty acids by active BAT may be detected as a decrease in the FSF. This decrease in FSF is seen in our results, where the FSF is on average 2.2% lower after exposure to cold than to warm temperatures, similar to previously published results (44). Although the FSF values presented here are lower than those reported by Lundström et al (44), this is likely because of the difference in the manner in which the BAT masks or regions of interest (ROIs) were defined.…”

“…These findings support MRI as a viable option for studying BAT in adult humans. Additionally, this study extends previous MRI research to quantitatively measure differences in FSF and R 2 * values in supraclavicular and subcutaneous adipose tissue depots (30,44). To the best of our knowledge, this work represents the first study to quantify PET-CT and MRI measurements and to utilize a semiautomated algorithm to identify BAT in the same adults after exposure to both thermoneutral and cold temperatures.…”

“…Although the FSF values presented here are lower than those reported by Lundström et al (44), this is likely because of the difference in the manner in which the BAT masks or regions of interest (ROIs) were defined. Lundström et al (44) used manual ROI definitions, whereas this work utilized PET-CT to restrict and define the spatial location of the BAT ROIs on the MRI. Therefore, we believe the ROIs used here are more rigorous and restrictive.…”

“…Therefore, we believe the ROIs used here are more rigorous and restrictive. It is possible that the ROIs used by Lundström et al (44) included tissue that was not BAT, resulting in a higher fat fraction. The goal of future work is to achieve full automation of BAT ROI definition.…”

Fat-Referenced MRI: Quanitaive MRI for Tissue Characterizaion and Volume Measurement

“…The goal was to study an intervention effect, and we had expected a stronger sBAT response following the cold adaptation. Other studies have shown that water-fat MRI is applicable to BAT characterization in adults [46,[100][101][102][103][104][105][106][107][108][109]. Thus, the weak effect observed in paper VI is ether caused by a lack of sBAT browning, or insufficient sensitivity combined with a weak intervention effect.…”