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AJR Am J Roentgenol. 2013 Oct;201(4):720-5. doi: 10.2214/AJR.12.10332.

Detection of implants and other objects using a ferromagnetic detection system: implications for patient screening before MRI.

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  • 11 Department of Radiology, Keck School of Medicine, University of Southern California and Institute for Magnetic Resonance Safety, Education, and Research, 7511 McConnell Ave, Los Angeles, CA 90045.



Ferromagnetic detection systems have been used to prevent accidents related to external ferromagnetic objects (e.g., pocket knives, hearing aids, and so on). If a ferromagnetic implant was missed during MRI screening, the ability to use a ferromagnetic detection system to discover the object in a patient before MRI could potentially avoid a serious injury, which has important implications for patient safety. Therefore, the purpose of this investigation was to use a ferromagnetic detection system to assess implants and other objects that may be encountered in patients referred for MRI procedures.


A "pillar-type" ferromagnetic detection system was used to evaluate 67 different implants and other objects (pulse generators [n = 43], electronic devices [n = 5], stents [n = 6], CSF shunt valves [n = 3], orthopedic implants [n = 3], bullets [n = 4], and others [n = 3]) that were attached to a volunteer subject's body to approximate a realistic in situ location. The subject with the test item approached the ferromagnetic detection system, rotated in front of it four times, and withdrew while the alarms were monitored and recorded.


There were 58 true-positive, four true-negative, no false-positive, and five false-negative findings. Thus, the sensitivity was 92% and the specificity was 100%.


These results indicated that, besides being used to identify external ferromagnetic objects, this ferromagnetic detection system may be a useful tool to screen patients referred for MRI examinations who may have implanted or embedded items. Further investigation to determine the use of this ferromagnetic detection system to detect additional implants in the clinical setting is warranted.

[PubMed - indexed for MEDLINE]
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