PET/MRI of glucose metabolic rate, lipid content and perfusion in human brown adipose tissue

This study evaluated the MRI-derived fat fraction (FF), from a Cooling-reheating protocol, for estimating the cold-induced brown adipose tissue (BAT) metabolic rate of glucose (MR(glu)) and changes in lipid content, perfusion and arterial blood volume (V(A)) within cervical-supraclavicular fat (sBAT). Twelve volunteers underwent PET/MRI at baseline, during cold exposure and reheating. For each temperature condition, perfusion and V(A) were quantified with dynamic [(15)O]water-PET, and FF, with water-fat MRI. MR(glu) was assessed with dynamic [(18)F]fluorodeoxyglucose-PET during cold exposure. sBAT was defined using anatomical criteria, and its subregion sBAT(HI), by MR(glu) > 11 μmol/100 cm(3)/min. For all temperature conditions, sBAT-FF correlated negatively with sBAT-MR(glu) (ρ ≤ − 0.87). After 3 h of cold, sBAT-FF decreased (− 2.13 percentage points) but tended to normalize during reheating although sBAT(HI)-FF remained low. sBAT-perfusion and sBAT-V(A) increased during cold exposure (perfusion: + 5.2 ml/100 cm(3)/min, V(A): + 4.0 ml/100 cm(3)). sBAT-perfusion remained elevated and sBAT-V(A) normalized during reheating. Regardless of temperature condition during the Cooling-reheating protocol, sBAT-FF could predict the cold-induced sBAT-MR(glu). The FF decreases observed after reheating were mainly due to lipid consumption, but could potentially be underestimated due to intracellular lipid replenishment. The influence of perfusion and V(A), on the changes in FF observed during cold exposure, could not be ruled out.