+ Risk of patient injury
- Patients and individuals with a history of previous injury by a metallic foreign body such as a bullet, shrapnel, or other metallic object could be at risk for serious injury in the MRI environment.1
- A foreign metallic body may cause damage as it moves due to the attraction of the magnetic field
- Excessive heating may occur if the object is made from conductive material
- The risk of injury is dependent on:1
- Properties of the object (ferromagnetic properties of the foreign body, geometry, dimensions)
- Strength of the magnetic field
- Location of the object (in or adjacent to a sensitive site of the body such as vital neural, vascular, or soft tissue structures)
- Amount of force with which the object is “fixed” or retained within the tissue (i.e., counter-force or retention force from scarring or encapsulation may prevent migration of the metal)
+ Screening follow-up questioning
- Patients with metallic foreign bodies are identified through a thorough standard screening process prior to entry into the MRI environment.
- All those with a history of potential ferromagnetic foreign object penetration must undergo further investigation before being permitted entrance to the MRI environment2
- The use of radiographic imaging is the technique of choice recommended to detect metallic foreign bodies for individuals and patients prior to admission to the MRI environment1
- Complementary methods of screening include patient history, prior CT or MRI studies of the questioned anatomic area, or access to written documentation as to the type of implant or foreign object that might be present2
- If no reliable patient metal exposure history can be obtained, and the MRI examination cannot be delayed, it is recommended that such patients be physically examined by Level 2 MRI personnel*.2
- All areas of scars or deformities whose origins are unknown and which may have been caused by ferromagnetic foreign bodies are subject to radiographic imaging
- All patients also undergo radiographic imaging of the skull, orbits, chest, abdomen or pelvis to exclude metallic foreign objects
Special considerations for foreign orbital bodies
- Studies of screening for metallic foreign body in the orbit show that simple screening questions to determine the need for radiographic investigation increase the efficiency and cost-effectiveness of the screening process.1
- Patients with a suspected metallic foreign body in the orbit are asked about potential injuries to the eye, including:1
- History of eye injury
- Whether they had a medical examination at the time of injury
- Whether they were told by the examining physician that the foreign body or metallic fragment was removed in its entirety (“Did the doctor get it all out?”)
- If the patient did not have an injury, was told that their ophthalmologic examination was normal, and/or if the foreign body was removed entirely at the time of the injury, then he/she can proceed to MRI imaging.1
- If the answer to any of these questions leaves any doubt about the presence of a metallic foreign body in the orbit, radiographic imaging is recommended for further investigation.1
* Level 2 MRI personnel are defined as those with MRI safety education to ensure safety of all individuals and facility resources within the MRI environment
+ Unanticipated foreign bodies
- It is possible that during the course of a MRI examination an unanticipated ferromagnetic implant or foreign body is discovered.
- This is typically suspected or detected by means of a sizable field-distorting artifact
- In such cases, the MRT notifies the radiologist immediately of the suspected findings.
- MRTs take care to remove the patient from the scanner, minimizing the risk of injury:
- Patient is removed slowly
- Patient body position parallel to the scanner is maintained during removal
- Patient is moved as far down the table as possible before transfer to a stretcher
- Once safely out of the scanner, the patient is taken out of the MRI scanning room
- Shellock FG. Reference Manual for Magnetic Resonance Safety, Implants, and Devices. 2013 Ed. Los Angeles, CA: Biomedical Research Publishing Group; 2013.
- Kanal E, Barkovich J, Bell C, et al. ACR Guidance Document on MR Safe Practices: 2013. J Magn Reson Imaging 2013;37:501-530.