Safety and reliability of Radio Frequency Identification Devices in Magnetic Resonance Imaging and Computed Tomography

Abstract

Background: Radio Frequency Identification (RFID) devices are becoming more and more essential for patient safety in hospitals. The purpose of this study was to determine patient safety, data reliability and signal loss wearing on skin RFID devices during magnetic resonance imaging (MRI) and computed tomography (CT) scanning.

Methods: Sixty RFID tags of the type I-Code SLI, 13.56 MHz, ISO 18000-3.1 were tested: Thirty type 1, an RFID tag with a 76 x 45 mm aluminum-etched antenna and 30 type 2, a tag with a 31 x 14 mm copper-etched antenna. The signal loss, material movement and heat tests were performed in a 1.5 T and a 3 T MR system. For data integrity, the tags were tested additionally during CT scanning. Standardized function tests were performed with all transponders before and after all imaging studies.

Results: There was no memory loss or data alteration in the RFID tags after MRI and CT scanning. Concerning heating (a maximum of 3.6 degrees C) and device movement (below 1 N/kg) no relevant influence was found. Concerning signal loss (artifacts 2 - 4 mm), interpretability of MR images was impaired when superficial structures such as skin, subcutaneous tissues or tendons were assessed.

Conclusions: Patients wearing RFID wristbands are safe in 1.5 T and 3 T MR scanners using normal operation mode for RF-field. The findings are specific to the RFID tags that underwent testing.

Figure 1

RFID tag (31 × 14 mm, Copper, etched).

Figure 2

Quantitative image artifacts. Both RFID tags shown on the top have been placed one after the other in the middle of the plastic grid, immersed in 1 g/L CuSO4 solution. Gradient echo and Spin echo sequences as described in the ASTM Standard F2119-01 have been performed. The upper row shows MR images of a 3 mm-thick slice through the tags, the middle row slices 5 mm below the tag and the last row shows an orthogonal slice through the tag. Signal void could be found only a few millimeters away from the tag. Reduced signal due to shielding of the RF field may produce darker shadows in slices up to 1 cm away.

Figure 3

Two RFIDs attached directly to the skin of a right wrist in a volunteer with the devices centered in a dedicated 8-channel wrist coil.

Figure 4

Qualitative image artifacts. MR imaging findings in a volunteer with the RFID tags positioned on the dorsum of the wrist (a, b) and on the volar aspect of the wrist (c, d). Axial T1-weighted spin-echo MR-image (600/13; number of signals acquired, 1; field of view, 90 mm) shows only minimal geometric distorsion and susceptibility artifacts on skin and underlying subcutaneous tissue (arrowheads) (a and c). Axial T2-weighted Flash2D gradient-echo MR-image (400/15; number of signals acquired, 2; field of view, 90 mm) shows increased susceptibility artifacts on skin and underlying subcutaneous tissue and tendons (arrows) (b and d). Interpretation of articular structures is not compromised.

Figure 5

Tissue heating near RFID tag, temperature development over time. Temperature increases next to the large RFID tag at different positions during an MR sequence in a 1.5 T whole-body MR scanner. The temperature increases have been normalized to 2 W/kg as requested by the ASTM Standard.