Induced radiofrequency fields in patients undergoing MRI (Magnetic Resonance Imaging) exams: insights for risk assessment
Abstract
Induced radiofrequency fields in patients undergoing MRI (Magnetic Resonance Imaging) exams: insights for risk assessment Aiping Yao, Manuel Murbach, Tolga Goren, Earl Zastrow, Wolfgang Kainz, Niels Kuster. Induced radiofrequency fields in patients undergoing MR examinations: insights for risk assessment. Phys Med Biol. 2021 Aug 25. doi: 10.1088/1361-6560/ac212d. Abstract Purpose: To characterize and quantify the induced radiofrequency (RF) E-fields and B1+rms fields in patients undergoing magnetic resonance (MR) examinations; to provide guidance on aspects of RF heating risks for patients with and without implants; and to discuss some strengths and limitations of safety assessments in current ISO, IEC, and ASTM standards to determine the RF heating risks for patients with and without implants. Methods: Induced E-fields and B1+rms fields during 1.5T and 3T MR examinations were numerically estimated for high-resolution patient models of the Virtual Population exposed to ten two-port birdcage RF coils from head to feet imaging landmarks over the full polarization space, as well as in surrogate ASTM phantoms. Results: Worst-case B1+rms exposure greater than 3.5µT (1.5T) and 2µT (3T) must be considered for all MR examinations at the Normal Operating Mode limit. Representative induced electric (E)-field and specific absorption rate (SAR) distributions under different clinical scenarios allow quick estimation of clinical factors of high and reduced exposure. B1 shimming can cause +6dB enhancements to E-fields along implant trajectories. The distribution and magnitude of induced E-fields in the ASTM phantom differ from clinical exposures and are not always conservative for typical implant locations. Conclusions: Field distributions in patient models are condensed, visualized for quick estimation of risks, and compared to those induced in the ASTM phantom. Induced E-fields in patient models can significantly exceed those in the surrogate ASTM phantom in some cases. In the recent 19e2 revision of the ASTMF2182 standard, the major shortcomings of previous versions have been addressed by requiring that the relationship between ASTM test conditions and in vivo tangential E-fields be established, e.g. numerically. With this requirement, the principal methods defined in the ASTM standard for passive implants are reconciled with those of the ISO10974 standard for active implantable medical devices. Open access paper: iopscience.iop.org
AI evidence extraction
Main findings
Numerical estimates for 1.5T and 3T MR exams indicated worst-case B1+rms exposures >3.5 µT (1.5T) and >2 µT (3T) should be considered at the Normal Operating Mode limit. B1 shimming could produce +6 dB enhancements to E-fields along implant trajectories. Induced E-field distributions and magnitudes in the ASTM phantom differed from clinical exposures and were not always conservative; in some cases patient-model induced E-fields significantly exceeded those in the surrogate phantom.
Outcomes measured
- Induced RF electric (E) fields
- B1+rms fields
- Specific absorption rate (SAR) distributions
- RF heating risk considerations for patients with and without implants
- Comparison of induced fields in patient models vs ASTM phantom
- Effect of B1 shimming on E-fields along implant trajectories
Limitations
- Numerical estimation/simulation study (no direct clinical measurements described in abstract)
- Sample size and specific model/phantom details not provided in abstract
- Findings depend on selected RF coils, imaging landmarks, and modeled polarization space
Suggested hubs
-
occupational-exposure
(0.2) Discusses RF safety standards and risk assessment context, though focused on patients rather than workers.
View raw extracted JSON
{
"study_type": "engineering",
"exposure": {
"band": "RF",
"source": "MRI",
"frequency_mhz": null,
"sar_wkg": null,
"duration": null
},
"population": "Patients undergoing MR examinations (modeled using high-resolution Virtual Population patient models); surrogate ASTM phantoms",
"sample_size": null,
"outcomes": [
"Induced RF electric (E) fields",
"B1+rms fields",
"Specific absorption rate (SAR) distributions",
"RF heating risk considerations for patients with and without implants",
"Comparison of induced fields in patient models vs ASTM phantom",
"Effect of B1 shimming on E-fields along implant trajectories"
],
"main_findings": "Numerical estimates for 1.5T and 3T MR exams indicated worst-case B1+rms exposures >3.5 µT (1.5T) and >2 µT (3T) should be considered at the Normal Operating Mode limit. B1 shimming could produce +6 dB enhancements to E-fields along implant trajectories. Induced E-field distributions and magnitudes in the ASTM phantom differed from clinical exposures and were not always conservative; in some cases patient-model induced E-fields significantly exceeded those in the surrogate phantom.",
"effect_direction": "unclear",
"limitations": [
"Numerical estimation/simulation study (no direct clinical measurements described in abstract)",
"Sample size and specific model/phantom details not provided in abstract",
"Findings depend on selected RF coils, imaging landmarks, and modeled polarization space"
],
"evidence_strength": "low",
"confidence": 0.7399999999999999911182158029987476766109466552734375,
"peer_reviewed_likely": "yes",
"keywords": [
"MRI",
"MR examinations",
"radiofrequency",
"induced electric field",
"B1+rms",
"SAR",
"RF heating",
"implants",
"ASTM phantom",
"ASTM F2182",
"ISO 10974",
"IEC",
"ISO",
"risk assessment",
"birdcage RF coil",
"Virtual Population"
],
"suggested_hubs": [
{
"slug": "occupational-exposure",
"weight": 0.200000000000000011102230246251565404236316680908203125,
"reason": "Discusses RF safety standards and risk assessment context, though focused on patients rather than workers."
}
]
}
AI can be wrong. Always verify against the paper.
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