Evaluation of RF Heating on Humerus Implant in Phantoms during 1.5T MR Imaging and Comparisons with Electromagnetic Simulation

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  • MURANAKA Hiroyuki
    Major in Medical Engineering and Technology, Graduate Course in Integrated Human Sciences Studies, Hiroshima International University Department of Radiology, Hiroshima Prefectural Rehabilitation Center
  • HORIGUCHI Takayoshi
    Major in Medical Engineering and Technology, Graduate Course in Integrated Human Sciences Studies, Hiroshima International University
  • USUI Shuji
    Major in Medical Engineering and Technology, Graduate Course in Integrated Human Sciences Studies, Hiroshima International University
  • UEDA Yoshitake
    Major in Medical Engineering and Technology, Graduate Course in Integrated Human Sciences Studies, Hiroshima International University
  • NAKAMURA Osamu
    ING Co., Ltd. Chuoh College of Medical Technology
  • IKEDA Fumiaki
    PHOTON Co., Ltd.
  • IWAKURA Ken
    PHOTON Co., Ltd.
  • NAKAYA Giichirou
    Josai College of Medical Arts and Sciences

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Abstract

Purpose: To evaluate the effect of radiofrequency (RF) heating on a metallic implant during magnetic resonance imaging (MRI), temperatures at several positions of an implant were measured, and results are compared with electromagnetic simulations using a finite element method.<br> Methods: A humerus nail implant made of stainless steel was embedded at various depths of tissue-equivalent gel-phantoms with loop (loop phantom) and partially cut loop (loop-cut phantom), and the phantoms were placed parallel to the static magnetic field of a 1.5T MRI device. Scans were conducted at maximum RF for 15 min, and temperatures were recorded with 2 RF-transparent fiberoptic sensors. Finally, electromagnetic-field analysis was performed.<br> Results: Temperatures increased at both ends of the implants at various depths, and temperature increase was suppressed with increasing depth. The maximum temperature rise was 12.3°C at the tip of the implant and decreased for the loop-cut phantom. These tendencies resembled the results of electromagnetic simulations.<br> Conclusion: RF heating was verified even in a nonmagnetizing metal implant in a case of excessive RF irradiation. Particularly, rapid temperature rise was observed at both ends of the implant having large curvatures. The difference in temperature increase by depth was found to reflect the skin-depth effect of RF intensity. Electromagnetic simulation was extremely useful for visualizing the eddy currents within the loop and loop-cut phantoms and for evaluating RF heating of a metallic implant for MRI safety.<br>

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