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 / Safety Assessment

Journal: Phys Med Biol

Institution: Virtual Population

DOI: 10.1088/1361-6560/ac212d

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

Abstract

Overview

The study aims to characterize and quantify the induced radiofrequency (RF) E-fields and B1+rms fields in patients undergoing magnetic resonance (MR) examinations. It provides comprehensive guidance on RF heating risks particularly for patients with and without implants and evaluates the adequacy of current safety standards.

Methods

  • Utilized high-resolution patient models from the Virtual Population.
  • Exposure scenarios included ten two-port birdcage RF coils, from head to feet imaging, across the full polarization space.
  • Assessment also in surrogate ASTM phantoms for comparison.

Findings

Indications show worst-case B1+rms exposure exceeds recommended limits in normal operating modes of MR systems, highlighting potential overexposure scenarios. Notably, B1 shimming might intensify E-field exposures along implant trajectories.

The study contrasts induced E-fields in clinical settings against those in ASTM phantoms, often finding substantial discrepancies which may not always be conservative for typical implant locations.

Conclusion

Fields in patient models are visualized for rapid risk estimation. The updated ASTMF2182 standards addressed many prior gaps by aligning test conditions more closely with real-world in vivo scenarios, therefore enhancing the relevance and protective scope of safety assessments for patients with implants during MR exams.

MRI radiofrequency fields RF heating risks safety standards implants electromagnetic fields health risk
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