title: MR-based attenuation correction for torso-PET/MR imaging: pitfalls in mapping MR to CT data.
abstract: OBJECTIVE
  MR-based attenuation correction (AC) will become an integral part of combined PET/MR systems. Here, we propose a toolbox to validate MR-AC of clinical PET/MRI data sets.
  
  
  METHODS
  Torso scans of ten patients were acquired on a combined PET/CT and on a 1.5-T MRI system. MR-based attenuation data were derived from the CT following MR-CT image co-registration and subsequent histogram matching. PET images were reconstructed after CT- (PET(CT)) and MR-based AC (PET(MRI)). Lesion-to-background (L/B) ratios were estimated on PET(CT) and PET(MRI).
  
  
  RESULTS
  MR-CT histogram matching leads to a mean voxel intensity difference in the CT- and MR-based attenuation images of 12% (max). Mean differences between PET(MRI) and PET(CT) were 19% (max). L/B ratios were similar except for the lung where local misregistration and intensity transformation leads to a biased PET(MRI).
  
  
  CONCLUSIONS
  Our toolbox can be used to study pitfalls in MR-AC. We found that co-registration accuracy and pixel value transformation determine the accuracy of PET(MRI).
authors.affiliation: Department of Nuclear Medicine, University Hospital, Hufelandstr 55, 45122, Essen, Germany. thomas.beyer@uni-due.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Beyer
authors.forename: Markus
authors.initials: M
authors.lastname: Weigert
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
authors.forename: Uwe
authors.initials: U
authors.lastname: Pietrzyk
authors.forename: Florian
authors.initials: F
authors.lastname: Vogt
authors.forename: Christoph
authors.initials: C
authors.lastname: Palm
authors.forename: Gerald
authors.initials: G
authors.lastname: Antoch
authors.forename: Stefan P
authors.initials: SP
authors.lastname: Müller
authors.forename: Andreas
authors.initials: A
authors.lastname: Bockisch
mesh_terms: D000465:Algorithms; D016477:Artifacts; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009369:Neoplasms / Q000175:diagnosis*; D049268:Positron-Emission Tomography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012984:Software; D013382:Subtraction Technique; D013909:Thorax; D014057:Tomography, X-Ray Computed / Q000379:methods*