title: Using the dGEMRIC technique to evaluate cartilage health in the presence of surgical hardware at 3T: comparison of inversion recovery and saturation recovery approaches.
abstract: OBJECTIVE
  To evaluate the effect of metal artifact reduction techniques on dGEMRIC T(1) calculation with surgical hardware present.
  
  
  METHODS
  We examined the effect of stainless-steel and titanium hardware on dGEMRIC T(1) maps. We tested two strategies to reduce metal artifact in dGEMRIC: (1) saturation recovery (SR) instead of inversion recovery (IR) and (2) applying the metal artifact reduction sequence (MARS), in a gadolinium-doped agarose gel phantom and in vivo with titanium hardware. T(1) maps were obtained using custom curve-fitting software and phantom ROIs were defined to compare conditions (metal, MARS, IR, SR).
  
  
  RESULTS
  A large area of artifact appeared in phantom IR images with metal when T(I) ≤ 700 ms. IR maps with metal had additional artifact both in vivo and in the phantom (shifted null points, increased mean T(1) (+151 % IR ROI(artifact)) and decreased mean inversion efficiency (f; 0.45 ROI(artifact), versus 2 for perfect inversion)) compared to the SR maps (ROI(artifact): +13 % T(1) SR, 0.95 versus 1 for perfect excitation), however, SR produced noisier T(1) maps than IR (phantom SNR: 118 SR, 212 IR). MARS subtly reduced the extent of artifact in the phantom (IR and SR).
  
  
  CONCLUSIONS
  dGEMRIC measurement in the presence of surgical hardware at 3T is possible with appropriately applied strategies. Measurements may work best in the presence of titanium and are severely limited with stainless steel. For regions near hardware where IR produces large artifacts making dGEMRIC analysis impossible, SR-MARS may allow dGEMRIC measurements. The position and size of the IR artifact is variable, and must be assessed for each implant/imaging set-up.
authors.affiliation: Department of Mechanical Engineering, University of British Columbia, Vancouver, BC, Canada, agnes.dentremont@gmail.com.
authors.forename: Agnes G
authors.initials: AG
authors.lastname: d'Entremont
authors.forename: Shannon H
authors.initials: SH
authors.lastname: Kolind
authors.forename: Burkhard
authors.initials: B
authors.lastname: Mädler
authors.forename: David R
authors.initials: DR
authors.lastname: Wilson
authors.forename: Alexander L
authors.initials: AL
authors.lastname: MacKay
mesh_terms: D016477:Artifacts; D001860:Bone Plates; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007719:Knee Joint / Q000033:anatomy & histology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods; D008875:Middle Aged; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013193:Stainless Steel; D014025:Titanium
chemical_list: D013193:Stainless Steel; D014025:Titanium