title: Hybrid PET/MRI as a tool to detect brown adipose tissue: Proof of principle.
abstract: 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 4mm 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 technique, as compared with PET/CT, includes a lower radiation burden, and the possibility to combine a multiparameter fat characterization by dedicated MRI sequences. Hybrid PET/MRI might represent the ideal tool for BAT evaluation.
authors.affiliation: Service of Internal Medicine, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland. Electronic address: Karim.Gariani@hcuge.ch.
authors.forename: Karim
authors.initials: K
authors.lastname: Gariani
authors.affiliation: Department of Radiology, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Gariani
authors.affiliation: Nuclear Medicine and Molecular Unit, Department of Medical Imaging, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Gaël
authors.initials: G
authors.lastname: Amzalag
authors.affiliation: Department of Radiology, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Bénédicte M A
authors.initials: BM
authors.lastname: Delattre
authors.affiliation: Nuclear Medicine and Molecular Unit, Department of Medical Imaging, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Osman
authors.initials: O
authors.lastname: Ratib
authors.affiliation: Nuclear Medicine and Molecular Unit, Department of Medical Imaging, Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Valentina
authors.initials: V
authors.lastname: Garibotto
mesh_terms: D002001:Adipose Tissue, Brown / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D000328:Adult; D000368:Aged; D003080:Cold Temperature; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000008:administration & dosage / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015994:Incidence; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000378:metabolism; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013557:Switzerland / Q000453:epidemiology; D022722:Thermogenesis; D014018:Tissue Distribution; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: Brown adipose tissue; Magnetic resonance imaging; Obesity; Positron emission tomography