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SCIENTIFIC EXHIBIT |
1 From the Departments of Radiology (R.V.O., P.L.M., M.J.L., D.L.J., A.L.M., Q.S.X.), Orthopedic Surgery (P.L.M., B.M.), and Physics and Astronomy (A.L.M., Q.S.X.), University of British Columbia, Vancouver General Hospital, 855 W 12th Ave, Vancouver, British Columbia, Canada V5Z 1M9; the Vancouver Musculoskeletal Tumor Group, Vancouver, British Columbia, Canada (P.L.M., M.J.L., B.M.); and the Department of Radiology, Surrey Memorial Hospital, Surrey, British Columbia, Canada (D.L.J.). Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received March 22, 1999; revision requested May 3 and received May 28; accepted June 1. Address reprint requests to P.L.M. (e-mail: plmunk@interchange.ubc.ca).
Artifact arising from metal hardware remains a significant problem in orthopedic magnetic resonance imaging. The metal artifact reduction sequence (MARS) reduces the size and intensity of susceptibility artifacts from magnetic field distortion. The sequence, which is based on view angle tilting in combination with increased gradient strength, can be conveniently used in conjunction with any spin-echo sequence and requires no additional imaging time. In patients with persistent pain after femoral neck fracture, the MARS technique allows visualization of marrow adjacent to hip screws, thus enabling diagnosis or exclusion of avascular necrosis. Other applications in the hip include assessment of periprosthetic soft tissues after hip joint replacement surgery, postoperative assessment after resection of bone tumors and reconstruction, and localization of unopacified methyl methacrylate cement prior to hip arthroplasty revision surgery. In the knee, the MARS technique allows visualization of structures adjacent to implanted metal staples, pins, or screws. The technique can significantly improve visualization of periprosthetic bone and soft-tissue structures even in patients who have undergone total knee arthroplasty. In patients with spinal fixation hardware, the MARS technique frequently allows visualization of the vertebral bodies and spinal canal contents. The technique can be helpful after wrist fusion or screw fixation of scaphoid fractures.
Index Terms: Hip, necrosis, 442.44 • Hip, surgery, 442.45 • Knee, surgery, 452.45 • Magnetic resonance (MR), artifact • Magnetic resonance (MR), pulse sequences • Metallic devices • Spine, fixation devices, 30.45
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