Metal artifact reduction sequence: Early clinical applications

Artifact arising from metal hardware remains a significant problem in ortho pedic magnetic resonance imaging. The metal artifact reduction sequence (MA RS) reduces the size and intensity of susceptibility artifacts from magneti c field distortion. The sequence, which is based on view angle tilting in c ombination with increased gradient strength, can be conveniently used in co njunction with any spin-echo sequence and requires no additional imaging ti me. In patients with persistent pain after femoral neck fracture, the MARS technique allows visualization of marrow adjacent to hip screws, thus enabl ing diagnosis or exclusion of avascular necrosis. Other applications in the hip include assessment of periprosthetic soft tissues after hip joint repl acement surgery, postoperative assessment after resection of bone tumors an d reconstruction, and localization of unopacified methyl methacrylate cemen t prior to hip arthroplasty revision surgery. In the knee, the MARS techniq ue allows visualization of structures adjacent to implanted metal staples, pins, or screws. The technique can significantly improve visualization of p eriprosthetic bone and soft-tissue structures even in patients who have und ergone 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.