Please cite this article in press as: Gariani K, et al. Hybrid PET/MRI as a tool to detect brown adipose tissue: Proof of principle. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.05.004 ARTICLE IN PRESS ORCP-454; No. of Pages 5 Obesity Research & Clinical Practice (2015) xxx, xxx—xxx SHORT REPORT Hybrid PET/MRI as a tool to detect brown adipose tissue: Proof of principle Karim Gariani a,* , Joanna Gariani b , Gaël Amzalag c , Bénédicte M.A. Delattre b , Osman Ratib c , Valentina Garibotto c a Service of Internal Medicine, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland b Department of Radiology, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland c Nuclear Medicine and Molecular Unit, Department of Medical Imaging, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland Received 11 February 2015 ; received in revised form 8 April 2015; accepted 7 May 2015 KEYWORDS Brown adipose tissue; Obesity; Positron emission tomography; Magnetic resonance imaging Summary Objective: The purpose of this study was to assess the performance of 18 F-FDG hybrid PET/MRI to detect and localise the presence of metabolically active brown adipose tissue (BAT). Methods: We retrospectively analyzed 197 consecutive 18 F-flurodeoxyglucose ( 18 F- FDG) positron-emission tomographic (PET) and magnetic resonance imaging (MRI) images performed with a hybrid whole-body PET—MRI tomography in 192 patients. These patients were originally investigated mainly for oncological staging, in the absence of a cooling protocol. The presence of BAT was defined as a soft tissue structure that was larger than 4 mm in diameter, had the characteristics of fat tissue on MRI and had a maximal standardised uptake value (SUV) of 18 F-FDG of at least 2.0. No specific MRI sequences for BAT detection were acquired. Results: PET/MRI identified the presence of metabolically active BAT in 5 out of 192 patients (2.6%). BAT positive subjects were all female, significantly younger and with significantly lower body weight than BAT negative subjects. Conclusions: Whole body hybrid PET/MRI allowed for the identification of BAT, with a low prevalence, comparable to previous retrospective PET/CT studies realised in the absence of a cooling protocol. The main advantages of the PET/MRI hybrid ∗ Corresponding author at: Service of Internal Medicine, Geneva University Hospital and Faculty of Medicine, Rue Gabrielle Perret- Gentil 4, Geneva, Switzerland. Tel.: +41 22 372 92 05; fax: +41 372 92 35. E-mail address: Karim.Gariani@hcuge.ch (K. Gariani). http://dx.doi.org/10.1016/j.orcp.2015.05.004 1871-403X/© 2015 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.