The orientation of orthopaedic metallic devices relative to the frequency-encoding gradient affects susceptibility artifacts: an experiment using open MR imaging.

Purpose: 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.

Materials And 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).

Conclusion: 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.