title: Iterative metal artifact reduction: evaluation and optimization of technique.
abstract: OBJECTIVE
  Iterative metal artifact reduction (IMAR) is a sinogram inpainting technique that incorporates high-frequency data from standard weighted filtered back projection (WFBP) reconstructions to reduce metal artifact on computed tomography (CT). This study was designed to compare the image quality of IMAR and WFBP in total shoulder arthroplasties (TSA); determine the optimal amount of WFBP high-frequency data needed for IMAR; and compare image quality of the standard 3D technique with that of a faster 2D technique.
  
  
  METHODS
  Eight patients with nine TSA underwent CT with standardized parameters: 140 kVp, 300 mAs, 0.6 mm collimation and slice thickness, and B30 kernel. WFBP, three 3D IMAR algorithms with different amounts of WFBP high-frequency data (IMARlo, lowest; IMARmod, moderate; IMARhi, highest), and one 2D IMAR algorithm were reconstructed. Differences in attenuation near hardware and away from hardware were measured and compared using repeated measures ANOVA. Five readers independently graded image quality; scores were compared using Friedman's test.
  
  
  RESULTS
  Attenuation differences were smaller with all 3D IMAR techniques than with WFBP (p < 0.0063). With increasing high-frequency data, the attenuation difference increased slightly (differences not statistically significant). All readers ranked IMARmod and IMARhi more favorably than WFBP (p < 0.05), with IMARmod ranked highest for most structures. The attenuation difference was slightly higher with 2D than with 3D IMAR, with no significant reader preference for 3D over 2D.
  
  
  CONCLUSIONS
  IMAR significantly decreases metal artifact compared to WFBP both objectively and subjectively in TSA. The incorporation of a moderate amount of WFBP high-frequency data and use of a 2D reconstruction technique optimize image quality and allow for relatively short reconstruction times.
authors.affiliation: Cleveland Clinic, Imaging Institute, 9500 Euclid Ave, A21, Cleveland, OH, 44195, USA, subhasn@ccf.org.
authors.forename: Naveen
authors.initials: N
authors.lastname: Subhas
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Primak
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Obuchowski
authors.forename: Amit
authors.initials: A
authors.lastname: Gupta
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Polster
authors.forename: Andreas
authors.initials: A
authors.lastname: Krauss
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Iannotti
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D000704:Analysis of Variance; D001178:Arthroplasty; D016477:Artifacts; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008670:Metals; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D008670:Metals