Does anyone make an MRI-compatible active tag for patient tracking, and how are tags affected by other imaging energy (for example, X-rays and ultrasound)?
I am unaware of any companies that manufacture tags compatible with magnetic resonance imaging (MRI) equipment, and I had not heard of anyone who had conducted testing on tags in an MRI device, so I reached out to Roger Stewart, president of Sourland Mountain Associates. During his career, Roger has served as the VP of engineering at Applied Wireless ID, the chief technology officer at Intelleflex and the VP of engineering and CTO at Alien Technology, so he's very knowledgeable.
Roger says it is extremely unlikely that an RFID tag would be permanently affected by either ultrasound or X-ray radiation. However, he says, "Putting an RFID tag into an operating MRI imager is a questionable idea, due to the extremely high magnetic fields involved. This could be dangerous—not just to the tag, but to the imager and the patient as well. At the very least, someone should carefully test it first."
After I connected with Roger, an article was published on precisely this subject: Safety and Reliability of Radio Frequency Identification Devices in Magnetic Resonance Imaging and Computed Tomography.
According to the article, 60 RFID tags all showed normal functioning after being tested with MR and CT scans. It concludes: "According to the ASTM standard, a device is considered as MR-safe if it causes no known hazards to patients in all MR environments. Since the RFID tag contains conducting materials, RFID may only be MR-conditional, meaning safe under certain conditions for MR imaging during the scan. Significant increasing of temperature and unexpected strong movements are potential risk factors for patients with an implant during MRI examination."
—Mark Roberti, Editor, RFID Journal
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