Induced radiofrequency fields in patients undergoing MRI (Magnetic Resonance Imaging) exams: insights for risk assessment

Authors: Aiping Yao, Manuel Murbach, Tolga Goren, Earl Zastrow, Wolfgang Kainz, Niels Kuster

Year: 2021 Aug 25

Category: Radiology

Journal: Phys Med Biol

DOI: 10.1088/1361-6560/ac212d

URL: https://iopscience.iop.org/article/10.1088/1361-6560/ac212d

Abstract

Overview

This study explores the induced radiofrequency (RF) electric fields and B1+rms fields in patients during magnetic resonance (MR) examinations, offering crucial insights for enhancing RF heating risk assessments.

Purpose

  • Characterize and quantify the induced RF E-fields and B1+rms fields during MR examinations.
  • Provide guidance on RF heating risks for patients with or without implants.
  • Discuss strengths and limitations of current safety standards (ISO, IEC, ASTM) in determining RF heating risks.

Methods

Numerical estimations of induced E-fields and B1+rms fields were performed using high-resolution patient models from the Virtual Population, covering imaging from head to feet. These estimates utilized ten two-port birdcage RF coils across the full polarization space, comparing these to results in surrogate ASTM phantoms.

Findings

  • Identified worst-case B1+rms exposure scenarios across different MR systems.
  • Developed representative models for quick estimation of clinical exposure factors, highlighting potential enhancements due to B1 shimming.
  • Noted significant discrepancies in induced E-field distributions between in-vivo patient models and ASTM phantoms, particularly concerning typical implant locations.

Conclusion

The study emphasizes the need for revised standards and more accurate in-vivo testing methodologies to ensure patient safety, particularly concerning the interactions between induced E-fields and implantable medical devices.

MRI radiofrequency electromagnetic fields safety implants RF heating risks standards assessment
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