RF Safety with Implants
Yigitcan Eryaman1
1University of Minnesota, United States

Synopsis

Keywords: Physics & Engineering: RF Safety

This talk will focus on radio-frequency (RF) safety issues related to imaging patients with metallic implants. Different investigation methods including full-wave electromagnetic simulations, simplified transmission line models, and transfer-function measurements will be covered. Effect of RF induced currents on MR image quality will also be presented. Finally, a variety of mitigation strategies at different field strengths will be introduced.

Overview

Radiofrequency (RF) currents induced on metallic implants can cause heating during MRI, potentially causing tissue damage [1]. Various approaches are adopted to investigate this issue in the literature. Transmission line and transfer function representation of devices [2, 3] allow local SAR and temperature prediction for an arbitrary trajectory as long as the incident electric field is known. More complex computational methods including full-wave EM simulations [4] as well as machine learning-based SAR estimation methods [5] are also presented in the literature. On the experimental front, numerous phantom and animal studies [6-9] have been conducted to investigate this important safety problem. Today various monitoring and mitigation strategies exist to tackle the RF safety issues related to imaging implants. Fast, low power MR scans can be conducted to collect information regarding the heating risks for a specific scan scenario [9]. The device itself can be modified in order to monitor and mitigate the heating risks in a patient-specific manner [10, 11]. Finally, RF excitation methods can be optimized to reduce the heating risks and image artifacts substantially [12-14].

Acknowledgements

No acknowledgement found.

References

1)Henderson JM, Tkach J, Phillips M, Baker K, Shellock FG, Rezai AR. Permanent neurological deficit related to magnetic resonance imaging in a patient with implanted deep brain stimulation electrodes for Parkinson's disease: case report. Neurosurgery. 2005;57(5):

2)Acikel, V. and Atalar, E. (2011), Modeling of radio-frequency induced currents on lead wires during MR imaging using a modified transmission line method. Med. Phys., 38: 6623-6632. https://doi.org/10.1118/1.3662865

3)Park SM, Kamondetdacha R, Nyenhuis JA. Calculation of MRI-induced heating of an implanted medical lead wire with an electric field transfer function. J Magn Reson Imaging. 2007;26(5):1278-1285. doi:10.1002/jmri.21159

4)Guerin B, Iacono MI, Davids M, Dougherty D, Angelone LM, Wald LL. The 'virtual DBS population': five realistic computational models of deep brain stimulation patients for electromagnetic MR safety studies. Phys Med Biol. 2019;64(3):035021.

5)Vu, Jasmine, Bach T. Nguyen, Bhumi Bhusal, Justin Baraboo, Joshua Rosenow, Ulas Bagci, Molly G. Bright, and Laleh Golestanirad. "Machine learning-based prediction of MRI-induced power absorption in the tissue in patients with simplified deep brain stimulation lead models." IEEE transactions on electromagnetic compatibility 63, no. 5 (2021): 1757-1766.

6)Yeung CJ, Susil RC, Atalar E. RF heating due to conductive wires during MRI depends on the phase distribution of the transmit field. Magn Reson Med. 2002;48(6):1096-1098. doi:10.1002/mrm.10310

7)Rezai AR, Finelli D, Nyenhuis JA, et al. Neurostimulation systems for deep brain stimulation: in vitro evaluation of magnetic resonance imaging-related heating at 1.5 tesla. J Magn Reson Imaging. 2002;15(3):241-250. doi:10.1002/jmri.10069

8)Shrivastava, Devashish, Aviva Abosch, John Hughes, Ute Goerke, Lance DelaBarre, Rachana Visaria, Noam Harel, and J. Thomas Vaughan. "Heating induced near deep brain stimulation lead electrodes during magnetic resonance imaging with a 3 T transceive volume head coil." Physics in Medicine & Biology 57, no. 17 (2012): 5651.

9)Sadeghi-Tarakameh A, Zulkarnain NIH, He X, Atalar E, Harel N, Eryaman Y. A workflow for predicting temperature increase at the electrical contacts of deep brain stimulation electrodes undergoing MRI. Magn Reson Med. 2022;88(5):2311-2325. doi:10.1002/mrm.29375

10)Acikel, V., Silemek, B., & Atalar, E. (2020). Wireless control of induced radiofrequency currents in active implantable medical devices during MRI. Magnetic Resonance in Medicine, 83(6), 2370-2381.

11)Silemek, Berk, Frank Seifert, Johannes Petzold, Werner Hoffmann, Harald Pfeiffer, Oliver Speck, Georg Rose, Bernd Ittermann, and Lukas Winter. "Rapid safety assessment and mitigation of radiofrequency induced implant heating using small root mean square sensors and the sensor matrix Qs." Magnetic resonance in medicine 87, no. 1 (2022): 509-527.

12)Bachschmidt, Theresa J., Michael Köhler, Jürgen Nistler, Christian Geppert, Peter M. Jakob, and Mathias Nittka. "Polarized multichannel transmit MRI to reduce shading near metal implants." Magnetic Resonance in Medicine 75, no. 1 (2016): 217-226.

13)Ellenor, Christopher W., Pascal P. Stang, Maryam Etezadi‐Amoli, John M. Pauly, and Greig C. Scott. "Offline impedance measurements for detection and mitigation of dangerous implant interactions: An RF safety prescreen." Magnetic resonance in medicine 73, no. 3 (2015): 1328-1339.

14)Eryaman Y, Kobayashi N, Moen S, et al. A simple geometric analysis method for measuring and mitigating RF induced currents on Deep Brain Stimulation leads by multichannel transmission/reception. Neuroimage. 2019;184:658-668. doi:10.1016/j.neuroimage.2018.09.072

Proc. Intl. Soc. Mag. Reson. Med. 31 (2023)