Simulated radiation levels and patterns of MRI without a Faraday shielded room
Name
Magnetic Resonance in Med - 2025 - Kazemivalipour - Simulated radiation levels and patterns of MRI without a Faraday.pdf
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3.82 MB
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Author(s)
Kazemivalipour, Ehsan
Guerin, Bastien
Wald, Lawrence L.
Date Issued
March 17, 2025
Journal
Magnetic Resonance in Medicine
Publisher
Wiley
Citation
Kazemivalipour E, Guerin B, Wald LL. Simulated radiation levels and patterns of MRI without a Faraday shielded room. Magn Reson Med. 2025; 94: 835-851.
Version
Final published version
Abstract
Purpose: We characterize electromagnetic (EM) radiation patterns and levelsin conventional MRI systems as a function of field strength and load symmetry,providing a framework for mitigation strategies allowing operation without ashielded room.
Methods: We simulated the far-field radiation pattern and fields at a 10 mradius (|E|10m and |B|10m ) for a solenoidal superconducting MRI with abody birdcage coil operated between 0.25T and 6.5T. Five load configura-tions probed the impact of load-symmetry, ranging from a sphere to a bodyload (least-symmetric). We also assessed simple layered EM absorbers at thebore-ends.
Results: All configurations exceeded regulatory limits for realistic transmit lev-els. At 1.5T, a 300 V rms RF-pulse is 2700-fold the |E|10m limit. Field strengthand load symmetry strongly modulate radiation patterns and levels. The radi-ated power increased by more than four orders of magnitude from 0.25T to6.5T. Spherical load radiation transitioned from a peak gain at the bore-ends(0.25–0.5T) to a donut-shaped pattern, suggesting current loops around the bore(1 T–1.5T), back to bore-axis-directed gain, suggesting propagating waves alongthe bore (2T–6.5T). Transition patterns were seen between these regimes; uni-form radiation at 0.75T and a combined donut/bore-directed pattern at 1.75T.Load asymmetry increased both strength and pattern asymmetry, with the bodyload having the highest and least symmetric radiation with the legs facilitat-ing wave propagation at high-fields. A simple optimized layered absorber atscanner’s service-end reduced 3T peak radiation by 11 dB.
Conclusion: Radiation from unshielded scanners far exceeds regulatory lim-its, particularly at high-field. Mitigation strategies must address load-symmetry,field strength, and wave effects.
MIT Department
Harvard-MIT Program in Health Sciences and Technology
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DOI of Published Version
https://doi.org/10.1002/mrm.30499
