title: MR-PET co-registration in upper abdominal imaging: quantitative comparison of two different T1-weighted gradient echo sequences: initial observations.
abstract: OBJECTIVE
  The purpose of this study is to quantitatively compare the accuracy of spatial registration of Cartesian breath-hold 3D-GRE and non-respiratory-triggered free-breathing radial 3D-GRE images with PET data acquisition on whole-body hybrid MR-PET system.
  
  
  METHODS
  Eight patients (six men and two women; mean age, 56.6 ± 5.5 years) with nine ablated hepatocellular carcinomas constituted our study population. Spatial coordinates (x, y, z) of the estimated isocenters of the ablated areas were independently determined by two radiologists. Both T1-weighted sequences were performed in the axial plane. Distance between the isocenter of the lesion on PET images and on both T1-weighted images was measured, and misregistration was calculated. Statistical analysis was performed using Student t test.
  
  
  RESULTS
  Misalignment values of the hepatic ablation zones between PET and MR images were calculated at 4.94 ± 1.35 mm (reader 1) and 4.89 ± 2.21 mm (reader 2) for Cartesian 3D-GRE sequence, and 2.48 ± 0.65 mm (reader 1) and 2.72 ± 0.44 mm (reader 2) for the radial 3D-GRE sequence, with p values of 0.0011 and 0.0133, respectively.
  
  
  CONCLUSIONS
  Radial 3D-GRE offers improved registration accuracy with PET, supporting the use of this T1-weighted sequence in upper abdominal MR-PET studies.
authors.affiliation: Department of Radiology, University Of North Carolina at Chapel Hill, Old Clinic Bldg., CB 7510 - 2001, Chapel Hill, NC, 27599-7510, USA.
authors.forename: Miguel
authors.initials: M
authors.lastname: Ramalho
authors.forename: Mamdoh
authors.initials: M
authors.lastname: AlObaidy
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Burke
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dale
authors.forename: Kiran K
authors.initials: KK
authors.lastname: Busireddy
authors.forename: Terence Z
authors.initials: TZ
authors.lastname: Wong
authors.forename: Abdulaziz
authors.initials: A
authors.lastname: AlSugair
authors.forename: Richard C
authors.initials: RC
authors.lastname: Semelka
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging / Q000473:pathology; D006528:Carcinoma, Hepatocellular / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000473:pathology; D008113:Liver Neoplasms / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D015588:Observer Variation; D049268:Positron-Emission Tomography; D015203:Reproducibility of Results; D051598:Whole Body Imaging