Swiss Study Finds RFID Tags Safe for MRI, CT Scans
Researchers at St. Gallen Canton Hospital say that wristbands with 13.56 MHz passive RFID tags do not significantly interfere with the functionality of imaging devices, or pose a risk to scanned patients wearing such wristbands.
Mar 08, 2010—Researchers at St. Gallen Canton Hospital, in Switzerland, have found that high-frequency (HF) 13.56 MHz RFID tags do not significantly interfere with the functionality of imaging devices, nor do those devices affect the tags' functionality. The study, undertaken by physicians and researchers at the hospital and at the University of ETH Zurich, found that magnetic resonance imaging (MRI) radiation could raise the temperature of tissue around an RFID tag by, at most, 4 degrees Celsius (7 degrees Fahrenheit), but had no effect on a patient's health.
The quality of the MRI images was minimally impaired by the RFID tag's presence, the researchers report, and was limited to the area of the skin on which it was attached. Furthermore, the tag had no effect on a computed tomography (CT) scan's image quality. The results were published last month by Patient Safety in Surgery, an online peer-reviewed medical journal.
The study's results, according to the project's lead researcher, surgeon Thomas Steffen, prove that RFID wristbands can safely remain on a patient as he or she undergoes diagnostic procedures, such as MRI and CT scans. Steffen first conceived of the study in early 2009, to address the lack of evidence regarding the functionality and potential for safety or health hazards with the use of RFID in combination with MRI or CT scans. The researchers did note, however, the existence of a prior study examining the effects of MR scans on low-frequency passive RFID tags implanted under the skin (see Magnetic Resonance Imaging & VeriChip RFID Human Implant at 1.5 Tesla).
The researchers chose to test tags that operate at 13.56 MHz because that is the RFID frequency most commonly used in patient wristbands. The study involved 60 HF 13.56 MHz tags made with NXP Semiconductors' ICode SLI chips, and compliant with the ISO 15693 and ISO 18000-3 standards, in two sizes—half of them with 76-by-45-millimeter (3-by-2-inch) etched aluminum antennas, the other half with 31-by-14 millimeter (1-by-0.6-inch) etched copper antennas. Christian Kern, RFID solutions provider InfoMedis' chief technology officer, was the study's coauthor, and contributed the RFID tags and consultation regarding their usage.
In order to perform a reliability test with the RFID transponders, 15 of each of the two tag types were first read using Feig Electronic's Obid-MR100 interrogators, then 15 of each size were scanned by an MRI machine, and then by a CT machine, after which they were read once more. In groups of five, the RFID tags were attached to the sides of a 300-by-215-by-80-millimeter (9-by-8.5-by-4-inch) cardboard box, and were then scanned. A standardized scanning protocol was employed during MRI and CT scanning under the same conditions that would be present during a patient examination. The test was performed twice, for a total of 60 tag tests.
When testing tags mounted on cardboard boxes, the researchers utilized a CT scanner, as well as 1.5- and 3.0-tesla MRI scanners, employing the standard protocol for a cranial examination. The team also put some tags through "worst-case" sequences, in which they were subjected to MRI imaging for up to two hours. After being exposed to the magnetic fields of the MRI machines and the X-ray radiation of the CT machine—including the worst-case scenario—none of the tags showed any loss of function or alteration of the data (a unique ID number), Steffen says.
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