title: Investigating the state-of-the-art in whole-body MR-based attenuation correction: an intra-individual, inter-system, inventory study on three clinical PET/MR systems.
abstract: OBJECTIVE
  We assess inter- and intra-subject variability of magnetic resonance (MR)-based attenuation maps (MRμMaps) of human subjects for state-of-the-art positron emission tomography (PET)/MR imaging systems.
  
  
  METHODS
  Four healthy male subjects underwent repeated MR imaging with a Siemens Biograph mMR, Philips Ingenuity TF and GE SIGNA PET/MR system using product-specific MR sequences and image processing algorithms for generating MRμMaps. Total lung volumes and mean attenuation values in nine thoracic reference regions were calculated. Linear regression was used for comparing lung volumes on MRμMaps. Intra- and inter-system variability was investigated using a mixed effects model.
  
  
  RESULTS
  Intra-system variability was seen for the lung volume of some subjects, (p = 0.29). Mean attenuation values across subjects were significantly different (p < 0.001) due to different segmentations of the trachea. Differences in the attenuation values caused noticeable intra-individual and inter-system differences that translated into a subsequent bias of the corrected PET activity values, as verified by independent simulations.
  
  
  CONCLUSIONS
  Significant differences of MRμMaps generated for the same subjects but different PET/MR systems resulted in differences in attenuation correction factors, particularly in the thorax. These differences currently limit the quantitative use of PET/MR in multi-center imaging studies.
authors.affiliation: Center for Medical Physics and Biomedical Engineering, General Hospital Vienna, Medical University of Vienna, Waehringer Guertel 18-20/4L, 1090, Vienna, Austria. thomas.beyer@meduniwien.ac.at.
authors.forename: Thomas
authors.initials: T
authors.lastname: Beyer
authors.affiliation: Center for Medical Physics and Biomedical Engineering, General Hospital Vienna, Medical University of Vienna, Waehringer Guertel 18-20/4L, 1090, Vienna, Austria.
authors.forename: Martin L
authors.initials: ML
authors.lastname: Lassen
authors.affiliation: Department of Radiology and Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands. r.boellaard@umcg.nl.|Department of Nuclear Medicine and Molecular Imaging, University Medical Centre Groningen, Groningen, The Netherlands. r.boellaard@umcg.nl.
authors.forename: Ronald
authors.initials: R
authors.lastname: Boellaard
authors.affiliation: Department of Medical Imaging, University Hospital of Zurich, Zurich, Switzerland.|GE Healthcare, Waukesha, WI, USA.
authors.forename: Gaspar
authors.initials: G
authors.lastname: Delso
authors.affiliation: Department of Radiology and Nuclear Medicine, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Maqsood
authors.initials: M
authors.lastname: Yaqub
authors.affiliation: Department of Nuclear Medicine, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Sattler
authors.affiliation: Institute of Medical Physics, University of Erlangen-Nürnberg, Erlangen, Germany.|High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
mesh_terms: D000328:Adult; D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008168:Lung / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D015203:Reproducibility of Results; D051598:Whole Body Imaging / Q000379:methods
keywords: Accuracy; Combined PET/MR; MR-based attenuation correction; Reproducibility; Whole-body hybrid imaging