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

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. 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. 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). 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.