Screening Patients and Individuals with Metallic Foreign Bodies

Patients and individuals with a history of being injured by a metallic foreign body such as a bullet, shrapnel, or metallic object should be thoroughly screened and evaluated prior to admission to the area of the MR system.

This is particularly important because serious injury may occur as a result of movement or dislodgement of the metallic foreign body as it is attracted by the powerful magnetic field of the scanner. In addition, excessive heating may occur, although this tends to happen only if the object is made from conductive material and has an elongated shape or forms a loop with certain dimensions.

The relative risk of injury is dependent on the ferromagnetic properties of the foreign body, the geometry and dimensions of the object, the strength of the static magnetic field, and the strength of the spatial gradient of the magnet used for the MR system. Additionally, the potential for injury is related to the amount of force with which the object is fixed within the tissue (i.e., counter-force or retention force may prevent movement or dislodgement) and whether or not it is positioned in or adjacent to a sensitive site of the body. These sensitive sites include vital neural, vascular, or soft tissue structures.

The use of plain film radiography is the technique of choice recommended to detect metallic foreign bodies for individuals and patients prior to admission to the MRI environment.

This includes screening for the presence of metallic orbital foreign bodies (see Metallic Orbital Foreign Bodies and Screening). The inherent sensitivity of plain film radiography is considered to be sufficient to identify any metal with a mass large enough to present a hazard to an individual or patient in the MRI environment.

REFERENCES
Boutin, R. D., Briggs, J. E., and Williamson, M. R., Injuries associated with MR imaging: survey of safety records and methods used to screen patients for metallic foreign bodies before imaging. Am J Roentgenol 1994;162:189.

Dempsey MF, Condon B, Hadley DM. Investigation of the factors responsible for burns during MRI. J Magn Reson Imaging 2001;13:627-631.

Elster, A. D., Link, K. M., and Carr, J. J., Patient screening prior to MR imaging: a practical approach synthesized from protocols at 15 U.S. medical centers. Am J Roentgenol 1994;162:195.

International Commission on Non-Ionizing Radiation Protection (ICNIRP) Statement, Medical magnetic resonance procedures: protection of patients. Health Physics 2004;87:197-216.

Jarvik JG, Ramsey JG. Radiographic screening for orbital foreign bodies prior to MR imaging: Is it worth it? Am J Neuroradiol 2000;1:245.

Mani, R. L., In search of an effective screening system for intraocular metallic foreign bodies prior to MR - An important issue of patient safety. Am J Neuroradiol 1988;9:1032.

Murphy KJ, Burnberg JA. Orbital plain film as a prerequisite for MR imaging: is a known history of injury sufficient screening criteria? Am J Roentgenol 1996;167:1053.

Otto PM, et al. Screening test for detection of metallic foreign objects in the orbit before magnetic resonance imaging. Invest Radiol 1992;27:308-311.

Seidenwurm DJ, McDonnell CH, Raghavan N, Breslau J. Cost utility analysis of radiographic screening for an orbital foreign body before MR imaging. Am J Neuroradiol 2000;21:426.

Shellock FG, Kanal E. Magnetic resonance: Bioeffects, Safety and Patient Management, 2nd edition. Lippincott-Raven, New York, 1996.

Shellock FG. Magnetic Resonance Procedures: Health Effects and Safety. CRC Press, LLC, Boca Raton, FL, 2001.

Shellock FG, Crues JV. MR procedures: biologic effects, safety, and patient care. Radiology, 2004;232:635-652.

Shellock FG, Kanal E, SMRI Safety Committee. Policies, guidelines, and recommendations for MR imaging safety and patient management. J Magn Reson Imaging 1991;1:97-101.

Williams S, Char D H, Dillon WP, Lincoff N, Moseley M. Ferrous intraocular foreign bodies and magnetic resonance imaging. Am J Ophthalmology 1998;105:398.