The majority of pellets and bullets tested in the MR environment were found to be composed of nonferromagnetic materials, however, these items are often “contaminated” by ferromagnetic metals. Ammunition that proved to be ferromagnetic tended to be manufactured in foreign countries and/or used for military applications. Shrapnel typically contains steel and, therefore, presents a potential hazard for patients undergoing MR procedures.
Because pellets, bullets, and shrapnel are frequently contaminated with ferromagnetic materials, the risk versus benefit of performing an MR procedure should be carefully considered. Additional consideration must be given to whether the metallic object is located near or in a vital anatomic structure, with the assumption that the object is ferromagnetic and can potentially move, causing an injury. Additional consideration should be given to the length of time that the metallic foreign body has been present in the patient and to the possible presence of "counter-forces" provided by tissues that can prevent dislodgement in the presence of a strong magnetic field.
In an effort to reduce lead poisoning in “puddling” type ducks, the federal government requires many of the eastern United States to use steel shotgun pellets instead of lead. The presence of steel shotgun pellets presents a potential hazard to patients undergoing MR procedures and causes substantial imaging artifacts at the immediate position of these metallic objects. In one case, a small metallic BB located in a subcutaneous site caused painful symptoms in a patient exposed to an MR system, although no serious injury occurred. Accordingly, MR healthcare professionals should exercise caution when deciding to perform MR procedures in patients with pellets, bullets, shrapnel or other similar ballistic objects.
Smugar, et al. (1999) conducted an investigation to determine whether neurological problems developed in patients with intraspinal bullets or bullet fragments in association with MR imaging performed at 1.5-Tesla. Patients were queried during scanning for symptoms of discomfort, pain, or changes in neurological status. Additionally, detailed neurological examinations were performed prior to MRI, post MRI, and at the patients’ discharge. Based on these findings, Smugar, et al. concluded that a patient with a complete spinal cord injury may undergo MR imaging with an intraspinal bullet or fragment without concern for affects on the physical or neurological status. Thus, metallic fragments in the spinal canals of paralyzed patients are believed to represent only a relative contraindication to MR procedures.
Eshed, et al. (2010) conducted a retrospective investigation of the potential hazards for patients undergoing MRI at 1.5-Tesla with retained metal fragments from combat and terrorist attacks. Metallic fragments in 17 patients were in ranged in size between one and 10-mm. One patient reported a superficial migration of a 10-mm fragment after MRI. No other adverse reaction was reported. The authors concluded that 1.5-Tesla MRI examinations are safe in patients with retained metallic fragments from combat and terrorist attacks not in the vicinity of vital organs. However, caution is advised as well as an assessment of risk versus benefit for the patient.
Dedini, et al. (2013) studied bullets and shotgun pellets that were a representative sample of ballistic objects commonly encountered in association with criminal trauma using 1.5-, 3- and 7-Tesla MR systems. The findings indicated that non-steel containing bullets and pellets did not exhibit substantial magnetic field interactions at 1.5-, 3-, and 7-Tesla, and that both steel-containing and non-steel-containing bullets did not significantly heat, even under extreme MRI conditions at 3-Tesla. Steel-containing bullets were potentially unsafe for patients referred for MRI due to their potential to move in vivo, although this recommendation must be interpreted on a case-by-case basis with respect to the restraining effect of the specific tissue environment, time of the bullet in situ, proximity to vital or delicate structures, and with careful consideration given to the risk versus benefit for the patient.
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