title: Value of a Dixon-based MR/PET attenuation correction sequence for the localization and evaluation of PET-positive lesions.
abstract: OBJECTIVE
  In this study, the potential contribution of Dixon-based MR imaging with a rapid low-resolution breath-hold sequence, which is a technique used for MR-based attenuation correction (AC) for MR/positron emission tomography (PET), was evaluated for anatomical correlation of PET-positive lesions on a 3T clinical scanner compared to low-dose CT. This technique is also used in a recently installed fully integrated whole-body MR/PET system.
  
  
  METHODS
  Thirty-five patients routinely scheduled for oncological staging underwent (18)F-fluorodeoxyglucose (FDG) PET/CT and a 2-point Dixon 3-D volumetric interpolated breath-hold examination (VIBE) T1-weighted MR sequence on the same day. Two PET data sets reconstructed using attenuation maps from low-dose CT (PET(AC_CT)) or simulated MR-based segmentation (PET(AC_MR)) were evaluated for focal PET-positive lesions. The certainty for the correlation with anatomical structures was judged in the low-dose CT and Dixon-based MRI on a 4-point scale (0-3). In addition, the standardized uptake values (SUVs) for PET(AC_CT) and PET(AC_MR) were compared.
  
  
  RESULTS
  Statistically, no significant difference could be found concerning anatomical localization for all 81 PET-positive lesions in low-dose CT compared to Dixon-based MR (mean 2.51 ± 0.85 and 2.37 ± 0.87, respectively; p = 0.1909). CT tended to be superior for small lymph nodes, bone metastases and pulmonary nodules, while Dixon-based MR proved advantageous for soft tissue pathologies like head/neck tumours and liver metastases. For the PET(AC_CT)- and PET(AC_MR)-based SUVs (mean 6.36 ± 4.47 and 6.31 ± 4.52, respectively) a nearly complete concordance with a highly significant correlation was found (r = 0.9975, p < 0.0001).
  
  
  CONCLUSIONS
  Dixon-based MR imaging for MR AC allows for anatomical allocation of PET-positive lesions similar to low-dose CT in conventional PET/CT. Thus, this approach appears to be useful for future MR/PET for body regions not fully covered by diagnostic MRI due to potential time constraints.
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany. matthias.eiber@tum.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Eiber
authors.forename: Axel
authors.initials: A
authors.lastname: Martinez-Möller
authors.forename: Michael
authors.initials: M
authors.lastname: Souvatzoglou
authors.forename: Konstantin
authors.initials: K
authors.lastname: Holzapfel
authors.forename: Anja
authors.initials: A
authors.lastname: Pickhard
authors.forename: Dennys
authors.initials: D
authors.lastname: Löffelbein
authors.forename: Ivan
authors.initials: I
authors.lastname: Santi
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Rummeny
authors.forename: Sibylle
authors.initials: S
authors.lastname: Ziegler
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.forename: Stephan G
authors.initials: SG
authors.lastname: Nekolla
authors.forename: Ambros J
authors.initials: AJ
authors.lastname: Beer
mesh_terms: D000328:Adult; D000368:Aged; D001692:Biological Transport; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000503:physiopathology; D049268:Positron-Emission Tomography / Q000379:methods*; D011446:Prospective Studies; D012119:Respiration; D014057:Tomography, X-Ray Computed