ABSTRACT
Because of the streak artifacts associated with metallic objects, it is often difficult to interpret CT scans of patients with extensive surgical clips and hip prostheses. Streak artifacts can result from subtle motion of the metal during CT scanning, coupled with the large gradient between the metallic implant and the surrounding normal soft tissue. The magnetic field of the NMR scanner acts on all ferromagnetic objects within a given range. A potential hazard for patients examined with NMR arises from the longitudinal forces and torques exerted on ferromagnetic implants such as aneurysm clips. A wide range of metallic prostheses is available. They are composed of either stainless steel or titanium- or cobalt-based alloys. The necessity of protecting patients with implanted pacemakers from the static and time-varying fields of NMR is an important consideration in its planning and installation. Fortunately, outside the bore of the magnet, the hazards to the pacemaker recipient are well understood and not especially severe.
