title: The orientation of orthopaedic metallic devices relative to the frequency-encoding gradient affects susceptibility artifacts: an experiment using open MR imaging.
abstract: OBJECTIVE
  To evaluate the magnetic susceptibility artifacts associated with different frequency-encoding gradient directions for an angled cephalomedullary device of the proximal femur, and to determine the optimal extremity positioning for reducing artifacts using 0.4 T open MR imaging.
  
  
  METHODS
  Two different angular devices made of titanium alloy and stainless steel were used. The images were obtained with the frequency-encoding gradient parallel to the rod (Group R) and parallel to the lag screw (Group L). The device positioning was altered in order to obtain images with frequency-encoding gradient parallel to the rod and parallel to the lag screw. The artifact areas associated with the whole device and the lag screw were statistically evaluated.
  
  
  RESULTS
  For both devices, the mean artifact area in Group L was significantly larger than that in Group R (p<0.05). However, the mean artifact area of the lag screw only in Group L was significantly smaller than that in Group R (p<0.05).
  
  
  CONCLUSIONS
  Susceptibility artifacts for angled cephalomedullary devices can be minimized when the frequency-encoding gradient is parallel to the long axis of the regions of interest. Open MR imaging enables us to obtain the optimal orientation for minimizing susceptibility artifacts.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka.
authors.forename: Naohide
authors.initials: N
authors.lastname: Takeuchi
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Mitsuyasu
authors.forename: Tomonori
authors.initials: T
authors.lastname: Nakanishi
authors.forename: Sumako
authors.initials: S
authors.lastname: Nishimura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimoto
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Higaki
authors.forename: Makoto
authors.initials: M
authors.lastname: Hashizume
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D016477:Artifacts; D001858:Bone Nails; D001863:Bone Screws; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D013193:Stainless Steel; D014025:Titanium
chemical_list: D013193:Stainless Steel; D014025:Titanium