title: Metallic foreign bodies in the orbits of patients undergoing MR imaging: prevalence and value of radiography and CT before MR.
abstract: OBJECTIVE
  The purpose of this study was to measure the prevalence of metallic foreign bodies in the orbits of 15,024 patients who were scheduled for MR imaging during a 4-year period and to determine if screening by plain radiography, CT, or both before MR imaging is efficacious.
  
  
  METHODS
  Records of 15,024 patients scheduled for MR imaging were reviewed. A total of 1593 patients who had identified themselves as being at risk for an intraorbital metallic foreign body had undergone plain radiography or CT of the orbits. Plain radiographs and/or CT scans of patients reported as having orbital metal were reviewed to confirm the presence of a metallic foreign body and to identify its location.
  
  
  RESULTS
  Metallic foreign bodies were discovered in 40 patients. Six of these patients had impaired vision in the involved eye. Ten patients had a metallic foreign body in or near the orbit but well away from the globe and were thought to be at low risk for movement of the foreign body as a result of MR imaging. The other 24 patients had metallic foreign bodies adjacent to or within the globe and were thought to be at risk for movement of the metallic foreign body as a result of MR imaging.
  
  
  CONCLUSIONS
  The prevalence of intraorbital metallic foreign bodies in our study population was low (0.27%). Even in those patients identified as being at risk, the prevalence was only 2.5%. Based on the number of MR examinations performed annually in the United States and on data indicating that no radiographic screening is performed at 5% of institutions, we extrapolate that more than 2400 patients with intraorbital metallic foreign bodies have undergone MR imaging since 1986 without report of injury. These data allow us to infer that the risk of eye damage for patients who have intraorbital metal is low and that radiographic screening before MR imaging is not needed as often as it is done.
authors.affiliation: Department of Radiology, University of New Mexico, School of Medicine, Albuquerque 87131-5336.
authors.forename: M R
authors.initials: MR
authors.lastname: Williamson
authors.forename: M C
authors.initials: MC
authors.lastname: Espinosa
authors.forename: R D
authors.initials: RD
authors.lastname: Boutin
authors.forename: W W
authors.initials: WW
authors.lastname: Orrison
authors.forename: B L
authors.initials: BL
authors.lastname: Hart
authors.forename: C A
authors.initials: CA
authors.lastname: Kelsey
mesh_terms: D001766:Blindness / Q000517:prevention & control; D005129:Eye Foreign Bodies / Q000000981:diagnostic imaging / Q000453:epidemiology*; D005131:Eye Injuries / Q000517:prevention & control; D005260:Female; D005547:Foreign Bodies / Q000000981:diagnostic imaging / Q000453:epidemiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects*; D008297:Male; D008670:Metals; D009915:Orbit; D015995:Prevalence; D012307:Risk Factors; D014057:Tomography, X-Ray Computed
chemical_list: D008670:Metals