title: Reduction of metal artifacts in patients with total hip arthroplasty with slice-encoding metal artifact correction and view-angle tilting MR imaging.
abstract: OBJECTIVE
  To compare the new "warp" sequence (slice-encoding metal artifact correction [SEMAC], view-angle tilting [VAT], and increased bandwidth) for the reduction of both through-plane and in-plane magnetic resonance (MR) artifacts with current optimized MR sequences in patients with total hip arthroplasty (THA).
  
  
  METHODS
  The institutional review board issued a waiver for this study. Forty patients with THA were prospectively included. SEMAC, VAT, and increased bandwidth were applied by using the warp turbo-spin-echo sequence at 1.5 T. Coronal short tau inversion-recovery (STIR)-warp and transverse T1-weighted warp (hereafter, T1-warp) images, as well as standard coronal STIR and transverse T1-weighted sequence images optimized with high bandwidth (STIR-hiBW and T1-hiBW), were acquired. Fifteen additional patients were examined to compare the T1-warp and T1-hiBW sequence with an identical matrix size. Signal void was quantified. Qualitative criteria (distinction of anatomic structures, blurring, and noise) were assessed on a five-point scale (1, no artifacts; 5, not visible due to severe artifacts) by two readers. Abnormal imaging findings were recorded. Quantitative data were analyzed with a t test and qualitative data with a Wilcoxon signed rank test.
  
  
  RESULTS
  Signal void around the acetabular component was smaller for STIR-warp than STIR-hiBW images (21.6 cm2 vs 42.4 cm2; P=.0001), and for T1-warp than T1-hiBW images (17.6 cm2 vs 20.2 cm2; P=.0001). Anatomic distinction was better on STIR-warp compared with STIR-hiBW images (1.9-2.8 vs 3.6-4.6; P=.0001), and on T1-warp compared with T1-hiBW images (1.3-2.8 vs 1.8-3.2; P<.002). Distortion, blurring, and noise were lower with warp sequences than with the standard sequences (P=.0001). Almost half of the abnormal imaging findings were missed on STIR-hiBW compared with STIR-warp images (55 vs 105 findings; P=.0001), while T1-hiBW was similar to T1-warp imaging (50 vs 55 findings; P=.06).
  
  
  CONCLUSIONS
  STIR-warp and T1-warp sequences were significantly better according to quantitative and qualitative image criteria, but a clinically relevant artifact reduction was only present for STIR images.
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, 8008 Zurich, Switzerland. reto.sutter@balgrist.ch
authors.forename: Reto
authors.initials: R
authors.lastname: Sutter
authors.forename: Erika J
authors.initials: EJ
authors.lastname: Ulbrich
authors.forename: Vladimir
authors.initials: V
authors.lastname: Jellus
authors.forename: Mathias
authors.initials: M
authors.lastname: Nittka
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D016477:Artifacts; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008670:Metals; D008875:Middle Aged; D011446:Prospective Studies; D018709:Statistics, Nonparametric
chemical_list: D008670:Metals