Improved Radiofrequency Safety Modelling in MRI Using In Vivo Measurements of Brain Conductivity
Abstract
Tissue electrical properties are required by electromagnetic simulation software to conduct radiofrequency (RF) safety studies. Values are commonly taken from existing databases of tissue properties, where brain conductivity was measured ex vivo. We hypothesize that using in vivo brain conductivity values, as reported in the recent literature on in vivo MRI measurements, can improve the accuracy of such simulations. Sixteen subjects were scanned at 3T to obtain experimental maps of the transmit RF field, B+1, of the head. Electromagnetic simulations were performed using biomodels with varying morphologies, using both a conventional (σex vivo = 0.46 S/m) and a modified brain conductivity (σin vivo = 0.70 S/m). A framework was developed to process the simulated B+1 fields, including a systematic method to combine the two excitation ports of the transmit coil model (accounting for different load impedances between simulation and experiment), geometric alignment, and scaling of the simulated fields, allowing a quantitative comparison of complex B+1 maps of the brain with experimental maps. Specific absorption rate (SAR) maps were also estimated by different methods, including a novel B+1‐derived formula. Normalized root‐mean‐squared errors between simulation and experiment, in the brain, were approximately 6% for B+1 magnitude. While head geometry mainly impacted the accuracy of B+1 magnitude, with errors up to 11% ( p = 0.007) between the best fitting human model and the worst one, brain electrical conductivity mainly impacted B+1 phase, with errors reduced by 48% when using instead of ( p = 0.0004). The agreement in average brain SAR, between simulation and experiment, was also improved, with differences reduced from 62% (σex vivo) to 22% (σin vivo). Using brain conductivity values from recent in vivo studies improves the accuracy of RF safety modelling. Trial Registration: ClinicalTrials.gov identifier: NCT04645628.
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BibTeX
@article{paillart2026improved,
title = {{Improved Radiofrequency Safety Modelling in MRI Using In Vivo Measurements of Brain Conductivity}},
author = {Guillaume Paillart and Zhongzheng He and Grecia Romero and Pauline Ferry and Khalid Ambarki and Paul Soullié and Jacques Felblinger and Freddy Odille},
journal = {NMR in Biomedicine},
year = {2026},
month = jun,
doi = {10.1002/nbm.70335},
url = {https://hal.science/hal-05742500v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Improved Radiofrequency Safety Modelling in MRI Using In Vivo Measurements of Brain Conductivity
AU - Guillaume Paillart
AU - Zhongzheng He
AU - Grecia Romero
AU - Pauline Ferry
AU - Khalid Ambarki
AU - Paul Soullié
AU - Jacques Felblinger
AU - Freddy Odille
PY - 2026
DA - 2026/06/23
JO - NMR in Biomedicine
DO - 10.1002/nbm.70335
UR - https://hal.science/hal-05742500v1
AB - Tissue electrical properties are required by electromagnetic simulation software to conduct radiofrequency (RF) safety studies. Values are commonly taken from existing databases of tissue properties, where brain conductivity was measured ex vivo. We hypothesize that using in vivo brain conductivity values, as reported in the recent literature on in vivo MRI measurements, can improve the accuracy of such simulations. Sixteen subjects were scanned at 3T to obtain experimental maps of the transmit RF field, B^+_1, of the head. Electromagnetic simulations were performed using biomodels with varying morphologies, using both a conventional (σex vivo = 0.46 S/m) and a modified brain conductivity (σin vivo = 0.70 S/m). A framework was developed to process the simulated B^+_1 fields, including a systematic method to combine the two excitation ports of the transmit coil model (accounting for different load impedances between simulation and experiment), geometric alignment, and scaling of the simulated fields, allowing a quantitative comparison of complex B^+_1 maps of the brain with experimental maps. Specific absorption rate (SAR) maps were also estimated by different methods, including a novel B^+_1‐derived formula. Normalized root‐mean‐squared errors between simulation and experiment, in the brain, were approximately 6% for B^+_1 magnitude. While head geometry mainly impacted the accuracy of B^+_1 magnitude, with errors up to 11% ( p = 0.007) between the best fitting human model and the worst one, brain electrical conductivity mainly impacted B^+_1 phase, with errors reduced by 48% when using instead of ( p = 0.0004). The agreement in average brain SAR, between simulation and experiment, was also improved, with differences reduced from 62% (σex vivo) to 22% (σin vivo). Using brain conductivity values from recent in vivo studies improves the accuracy of RF safety modelling. Trial Registration: ClinicalTrials.gov identifier: NCT04645628.
SN - 0952-3480
SN - 1099-1492
ER -