title: Total knee arthroplasty MRI featuring slice-encoding for metal artifact correction: reduction of artifacts for STIR and proton density-weighted sequences.
abstract: OBJECTIVE
  The purpose of this article is to compare slice-encoding for metal artifact correction (SEMAC) sequences versus optimized standard MRI sequences in patients with total knee arthroplasty (TKA).
  
  
  METHODS
  Forty-two patients with TKA underwent 1.5-T MRI. Sequences optimized for metal implant imaging (SEMAC) were compared with standard sequences optimized with high bandwidth for STIR and proton density (PD)-weighted images. In 29 patients, CT was available as reference standard. Signal void and insufficient fat saturation were quantified. Qualitative criteria (anatomy, distortion, blurring, and noise) were assessed on a 5-point scale (1, no artifacts; 5, severe artifacts) by two readers. Abnormal imaging findings were noted. A Student t test and a Wilcoxon signed rank test was used for statistics.
  
  
  RESULTS
  Signal void areas and insufficient fat saturation were smaller for the SEMAC sequences than for the optimized standard sequences (p ≤ 0.005 for all comparisons). Depiction of anatomic structures was better on STIR with SEMAC versus standard sequences optimized with high bandwidth (score range, 2.9-3.7 vs 4.2-4.9) and on PD-weighted imaging with SEMAC versus standard sequences optimized with high bandwidth (score range, 2.5-3.5 vs 3.1-3.8), which was statistically significant (p < 0.001 to p = 0.007 for different structures). Distortion and noise were lower for SEMAC than for the standard sequences (p ≤ 0.001), whereas no technique had a clear advantage for blurring. Detection of abnormal imaging findings was markedly increased for the SEMAC technique (p < 0.001) and was most pronounced for STIR images (98 and 74 findings for STIR with SEMAC for readers 1 and 2, respectively, vs 37 and 37 findings for readers 1 and 2, respectively, for STIR with standard sequences optimized with high bandwidth). Sensitivity for detection of periprosthetic osteolysis was improved for STIR with SEMAC (100% and 86% for readers 1 and 2, respectively) compared with STIR with standard sequences optimized with high bandwidth (14% and 29% for readers 1 and 2, respectively).
  
  
  CONCLUSIONS
  SEMAC sequences showed a statistically significant artifact reduction. The detection of clinically relevant findings such as periprosthetic osteolysis was markedly improved.
authors.affiliation: 1 Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, Zurich 8008, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Sutter
authors.forename: Roman
authors.initials: R
authors.lastname: Hodek
authors.forename: Sandro F
authors.initials: SF
authors.lastname: Fucentese
authors.forename: Mathias
authors.initials: M
authors.lastname: Nittka
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D016477:Artifacts; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008670:Metals; D008875:Middle Aged; D010014:Osteolysis / Q000175:diagnosis; D012680:Sensitivity and Specificity
chemical_list: D008670:Metals