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.