title: Post-processing water-fat imaging technique for fat suppression in a low-field MR imaging system, evaluation in patients with rheumatoid arthritis.
abstract: OBJECTIVE
  To evaluate the feasibility of the phase difference-based post-processing water-fat imaging method for fat suppression at low-field in imaging of arthritic joints.
  
  
  METHODS
  Thirty joints (wrist, 10; elbow, 10; knee, 10) in 30 patients with rheumatoid arthritis were imaged using a 0.23T MRI unit. Contrast-enhanced T1-weighted (T1w) three-dimensional (3D) gradient-echo (GRE) images with and without fat suppression along with short inversion time inversion-recovery (STIR) images were evaluated by two radiologists. Contrast-enhanced T1w 3D GRE images and corresponding post-processed fat-suppressed images were scored for conspicuity and delineation of enhancing synovial hypertrophy. The uniformity of fat suppression was evaluated between T1w 3D GRE fat-suppressed images and STIR images, and general image quality was estimated for all of the three techniques by consensus. For a quantitative analysis, the enhancing synovial hypertrophy-to-fat contrast-to-noise (CNR) values for the T1W 3D GRE images with and without fat suppression were measured. For comparison, synovial bright signal-to-fat CNR values for the STIR images were measured.
  
  
  RESULTS
  The post-processing water-fat imaging technique for fat suppression was successfully applied in all examinations. Conspicuity and delineation of enhancing tissue were superior in fat-suppressed T1w 3D GRE images compared to non-fat-suppressed images (P < 0.0001). As expected, the enhancing synovial hypertrophy tissue-to-fat CNRs were significantly higher in fat-suppressed T1w 3D GRE images compared to non-fat-suppressed images (P < 0.0001). General image quality was assessed to be best in non-fat-suppressed images, and the difference was significant compared to fat-suppressed images (P < 0.05) and STIR images (P < 0.05).
  
  
  CONCLUSIONS
  The phase difference-based post-processing water-fat imaging technique for fat suppression can be successfully used at low-field, and it provides high-quality fat suppression images in imaging of arthritic joints.
authors.affiliation: Department of Diagnostic Radiology, University Hospital of Oulu, Kajaanintie 50, FIN-90229 Oulu, Finland. kari.palosaari@oulu.fi
authors.forename: Kari
authors.initials: K
authors.lastname: Palosaari
authors.forename: Osmo
authors.initials: O
authors.lastname: Tervonen
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis*; D016477:Artifacts; D004551:Elbow Joint / Q000473:pathology; D055590:Electromagnetic Phenomena / Q000379:methods; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D007596:Joints / Q000473:pathology*; D007719:Knee Joint / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011786:Quality Control; D012680:Sensitivity and Specificity; D014867:Water; D014955:Wrist Joint / Q000473:pathology
chemical_list: D014867:Water