title: Material-Dependent Implant Artifact Reduction Using SEMAC-VAT and MAVRIC: A Prospective MRI Phantom Study.
abstract: The aim of this study was to compare the degree of artifact reduction in magnetic resonance imaging achieved with slice encoding for metal artifact correction (SEMAC) in combination with view angle tilting (VAT) and multiacquisition variable resonance image combination (MAVRIC) for standard contrast weightings and different metallic materials.
  
  
  
  Four identically shaped rods made of the most commonly used prosthetic materials (stainless steel, SS; titanium, Ti; cobalt-chromium-molybdenum, CoCr; and oxidized zirconium, oxZi) were scanned at 3 T. In addition to conventional fast spin-echo sequences, metal artifact reduction sequences (SEMAC-VAT and MAVRIC) with varying degrees of artifact suppression were applied at different contrast weightings (T1w, T2w, PDw). Two independent readers measured in-plane and through-plane artifacts in a standardized manner. In addition, theoretical frequency-offset and frequency-offset-gradient maps were calculated. Interobserver agreement was assessed using intraclass correlation coefficient.
  
  
  
  Interobserver agreement was almost perfect (intraclass correlation coefficient, 0.86-0.99). Stainless steel caused the greatest artifacts, followed by CoCr, Ti, and oxZi regardless of the imaging sequence. While for Ti and oxZi rods scanning with weak SEMAC-VAT showed some advantage, for SS and CoCr, higher modes of SEMAC-VAT or MAVRIC were necessary to achieve artifact reduction. MAVRIC achieved better artifact reduction than SEMAC-VAT at the cost of longer acquisition times. Simulations matched well with the apparent geometry of the frequency-offset maps.
  
  
  
  For Ti and oxZi implants, weak SEMAC-VAT may be preferred as it is faster and produces less artifact than conventional fast spin-echo. Medium or strong SEMAC-VAT or MAVRIC modes are necessary for significant artifact reduction for SS and CoCr implants.
authors.affiliation: From the *Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich; †Institute for Biomedical Engineering, University and ETH Zurich, Zurich; ‡Department of Radiology, Kantonsspital Muensterlingen, Muensterlingen; §University of Zurich, Zurich; and ∥Department of Radiology, Hospital and University of Bern, Inselspital, Bern, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Filli
authors.forename: Lukas
authors.initials: L
authors.lastname: Jud
authors.forename: Roger
authors.initials: R
authors.lastname: Luechinger
authors.forename: Daniel
authors.initials: D
authors.lastname: Nanz
authors.forename: Gustav
authors.initials: G
authors.lastname: Andreisek
authors.forename: Val M
authors.initials: VM
authors.lastname: Runge
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kozerke
authors.forename: Nadja A
authors.initials: NA
authors.lastname: Farshad-Amacker
mesh_terms: D016477:Artifacts; D002857:Chromium; D003035:Cobalt; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008670:Metals; D015588:Observer Variation; D019047:Phantoms, Imaging; D011446:Prospective Studies; D014025:Titanium
chemical_list: D008670:Metals; D002857:Chromium; D003035:Cobalt; D014025:Titanium