Magnetic resonance imaging cooling-reheating protocol indicates decreased fat fraction via lipid consumption in suspected brown adipose tissue.
OBJECTIVE
To 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.


METHODS
Nine 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).


RESULTS
sBAT-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).


CONCLUSIONS
The 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.
Department of Radiology, Uppsala University, Uppsala, Sweden.
Elin
E
Lundström
Department of Radiology, Uppsala University, Uppsala, Sweden; Department of Information Technology, Uppsala University, Uppsala, Sweden.
Robin
R
Strand
Department of Radiology, Uppsala University, Uppsala, Sweden.
Lars
L
Johansson
Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.
Peter
P
Bergsten
Department of Radiology, Uppsala University, Uppsala, Sweden.
Håkan
H
Ahlström
Department of Radiology, Uppsala University, Uppsala, Sweden.
Joel
J
Kullberg
D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000328:Adult; D003080:Cold Temperature; D005223:Fats / Q000378:metabolism*; D005260:Female; D006358:Hot Temperature; D006801:Humans; D050356:Lipid Metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D050151:Subcutaneous Fat / Q000378:metabolism; D014867:Water / Q000378:metabolism; D055815:Young Adult
D005223:Fats; D014867:Water