title: New MR imaging methods for metallic implants in the knee: artifact correction and clinical impact.
abstract: OBJECTIVE
  To evaluate two magnetic resonance imaging (MRI) techniques, slice encoding for metal artifact correction (SEMAC) and multiacquisition variable-resonance image combination (MAVRIC), for their ability to correct for artifacts in postoperative knees with metal.
  
  
  METHODS
  A total of 25 knees were imaged in this study. Fourteen total knee replacements (TKRs) in volunteers were scanned with SEMAC, MAVRIC, and 2D fast spin-echo (FSE) to measure artifact extent and implant rotation. The ability of the sequences to measure implant rotation and dimensions was compared in a TKR knee model. Eleven patients with a variety of metallic hardware were imaged with SEMAC and FSE to compare artifact extent and subsequent patient management was recorded.
  
  
  RESULTS
  SEMAC and MAVRIC significantly reduced artifact extent compared to FSE (P < 0.0001) and were similar to each other (P = 0.58), allowing accurate measurement of implant dimensions and rotation. The TKRs were properly aligned in the volunteers. Clinical imaging with SEMAC in symptomatic knees significantly reduced artifact (P < 0.05) and showed findings that were on the majority confirmed by subsequent noninvasive or invasive patient studies.
  
  
  CONCLUSIONS
  SEMAC and MAVRIC correct for metal artifact, noninvasively providing high-resolution images with superb bone and soft tissue contrast.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California, USA. tinac@stanford.edu
authors.forename: Christina A
authors.initials: CA
authors.lastname: Chen
authors.forename: Weitian
authors.initials: W
authors.lastname: Chen
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Goodman
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Koch
authors.forename: Wenmaio
authors.initials: W
authors.lastname: Lu
authors.forename: Anja C
authors.initials: AC
authors.lastname: Brau
authors.forename: Christine E
authors.initials: CE
authors.lastname: Draper
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D016477:Artifacts; D001706:Biopsy; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007717:Knee / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008670:Metals; D008875:Middle Aged; D019047:Phantoms, Imaging; D019736:Prostheses and Implants; D012984:Software
chemical_list: D008670:Metals