title: Fat-suppressed MR Imaging of the Spine for Metal Artifact Reduction at 3T: Comparison of STIR and Slice Encoding for Metal Artifact Correction Fat-suppressed T2-weighted Images.
abstract: OBJECTIVE
  To compare short tau inversion recovery (STIR) images with slice encoding for metal artifact correction (SEMAC)-corrected magnetic resonance imaging (MRI) of spectral presaturation with inversion recovery (SPIR) or inversion recovery (IR) at 3T in patients with metallic spinal instrumentation.
  
  
  METHODS
  Following institutional review board's approval, 71 vertebrae with interbody fixation in 26 patients who underwent transpedicular spondylodesis with spinal metallic prostheses were analyzed with SEMAC spinal MRI. All the fixated vertebrae were examined with STIR, and 41 vertebrae of 15 patients were scanned with SEMAC-SPIR T2-weighted MRI. The remaining 30 vertebrae of 11 patients were scanned with SEMAC-IR T2-weighted MRI. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images with a five-point scale that included artifact reduction around the metallic implant and visualization of the rod and pedicle. Quantitative assessments were performed by calculating the signal intensity ratio of the fixated vertebra and non-metallic vertebra and by calculating the signal-to-noise ratios (SNRs) of the vertebrae. A paired t-test was used for the statistical analyses.
  
  
  RESULTS
  The SEMAC-IR MRI had a significant decrease in the metallic artifact area (P < 0.05), while the SEMAC-SPIR MRI yielded significantly increased artifact areas (P < 0.05). However, the signal intensity ratios (i.e., metal-induced signal pile-up) were not significantly different (P > 0.05) between the STIR and SEMAC MRI. The SNR of the SEMAC MRI was significantly lower than the SNR of the STIR (P < 0.05). The metal artifact reduction scores were significantly higher in the SEMAC-SPIR MRI (P < 0.05).
  
  
  CONCLUSIONS
  Despite the relatively larger artifact size and lower SNRs, the SEMAC-SPIR MRI was superior to the other types of fat-suppressed MRI of SEMAC-IR or T2-weighted STIR MRI. However, the drawbacks of high signal pile-up, large artifact size, and relatively low SNRs require further investigation to determine the best method for fat-suppressed MRI of metallic implants.
authors.affiliation: Department of Radiology, Research Institute of Radiological Science, Medical Convergence Research Institute, and Severance Biomedical Science Institute, Yonsei University College of Medicine.
authors.forename: Young Han
authors.initials: YH
authors.lastname: Lee
authors.forename: Seok
authors.initials: S
authors.lastname: Hahn
authors.forename: Eunju
authors.initials: E
authors.lastname: Kim
authors.forename: Jin-Suck
authors.initials: JS
authors.lastname: Suh
mesh_terms: D000273:Adipose Tissue / Q000000981:diagnostic imaging; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D001853:Bone Marrow / Q000000981:diagnostic imaging; D001863:Bone Screws; D000069343:Bone-Implant Interface / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008670:Metals; D008875:Middle Aged; D012189:Retrospective Studies; D059629:Signal-To-Noise Ratio; D013123:Spinal Fusion / Q000295:instrumentation; D013131:Spine / Q000000981:diagnostic imaging*
chemical_list: D008670:Metals