title: View-Angle Tilting and Slice-Encoding Metal Artifact Correction for Artifact Reduction in MRI: Experimental Sequence Optimization for Orthopaedic Tumor Endoprostheses and Clinical Application.
abstract: BACKGROUND
  MRI plays a major role in follow-up of patients with malignant bone tumors. However, after limb salvage surgery, orthopaedic tumor endoprostheses might cause significant metal-induced susceptibility artifacts.
  
  
  OBJECTIVE
  To evaluate the benefit of view-angle tilting (VAT) and slice-encoding metal artifact correction (SEMAC) for MRI of large-sized orthopaedic tumor endoprostheses in an experimental model and to demonstrate clinical benefits for assessment of periprosthetic soft tissue abnormalities.
  
  
  METHODS
  In an experimental setting, tumor endoprostheses (n=4) were scanned at 1.5T with three versions of optimized high-bandwidth turbo-spin-echo pulse sequences: (i) standard, (ii) VAT and (iii) combined VAT and SEMAC (VAT&SEMAC). Pulse sequences included coronal short-tau-inversion-recovery (STIR), coronal T1-weighted (w), transverse T1-w and T2-w TSE sequences. For clinical evaluation, VAT&SEMAC was compared to conventional metal artifact-reducing MR sequences (conventional MR) in n=25 patients with metal implants and clinical suspicion of tumor recurrence or infection. Diameters of artifacts were measured quantitatively. Qualitative parameters were assessed on a five-point scale (1=best, 5=worst): "image distortion", "artificial signal changes at the edges" and "diagnostic confidence". Imaging findings were correlated with pathology. T-tests and Wilcoxon-signed rank tests were used for statistical analyses.
  
  
  RESULTS
  The true size of the prostheses was overestimated on MRI (P<0.05). A significant reduction of artifacts was achieved by VAT (P<0.001) and VAT&SEMAC (P=0.003) compared to the standard group. Quantitative scores improved in the VAT and VAT&SEMAC group (P<0.05). On clinical MR images, artifact diameters were significantly reduced in the VAT&SEMAC-group as compared with the conventional-group (P<0.001). Distortion and artificial signal changes were reduced and diagnostic confidence improved (P<0.05). In two cases, tumor-recurrence, in ten cases infection and in thirteen cases other pathologies were diagnosed.
  
  
  CONCLUSIONS
  Significant reduction of metallic artifacts was achieved by VAT and SEMAC. Clinical results suggest, that these new techniques will be beneficial for detecting periprosthetic pathologies during postoperative follow-up.
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Pia M
authors.initials: PM
authors.lastname: Jungmann
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Carl
authors.initials: C
authors.lastname: Ganter
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany; Musculoskeletal Imaging, Kantonsspital Graubuenden, Loestrasse 170, CH-7000, Chur, Switzerland.
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Schaeffeler
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany; Department of Neuroradiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Jan S
authors.initials: JS
authors.lastname: Bauer
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Baum
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Meier
authors.affiliation: Siemens AG, Healthcare Sector, Allee am Roethelheimpark 2, 91052, Erlangen, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Nittka
authors.affiliation: Department of Orthopaedic Surgery, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Pohlig
authors.affiliation: Department of Orthopaedic Surgery, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Rechl
authors.affiliation: Department of Orthopaedic Surgery, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Ruediger
authors.initials: R
authors.lastname: von Eisenhart-Rothe
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Rummeny
authors.affiliation: Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaninger Strasse 22, 81675, Munich, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Woertler
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D001859:Bone Neoplasms / Q000175:diagnosis / Q000601:surgery; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards*; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D009369:Neoplasms / Q000175:diagnosis* / Q000601:surgery; D009985:Orthopedics; D015203:Reproducibility of Results; D055815:Young Adult