Numerical and Experimental Analysis of Radiofrequency-Induced Heating Versus Lead Conductivity During EEG-MRI at 3 T

Seyed Reza Atefi; Peter Serano; Catherine Poulsen; Leonardo M Angelone; Giorgio Bonmassar

doi:10.1109/TEMC.2018.2840050

Numerical and Experimental Analysis of Radiofrequency-Induced Heating Versus Lead Conductivity During EEG-MRI at 3 T

IEEE Trans Electromagn Compat. 2019 Jun;61(3):852-859. doi: 10.1109/TEMC.2018.2840050. Epub 2018 Jun 25.

Authors

Seyed Reza Atefi¹, Peter Serano², Catherine Poulsen³, Leonardo M Angelone⁴, Giorgio Bonmassar⁵

Affiliations

¹ Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129 USA, and also with the University of Boras 50190, Boras Sweden (atefi@kth.se).
² Division of Biomedical Physics, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, MD 11401 USA (pete@serano.org).
³ Philips Neuro, Eugene, OR 97401 USA (catherine. poulsen@philips.com).
⁴ Division of Biomedical Physics, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, MD 11401 USA (Leonardo.Angelone@fda.hhs.gov).
⁵ Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129 USA (giorgio.bonmassar@mgh.harvard.edu).

Abstract

This study investigates radiofrequency (RF)-induced heating in a head model with a 256-channel electroencephalogram (EEG) cap during magnetic resonance imaging (MRI). Nine computational models were implemented each with different EEG lead electrical conductivity, ranging from 1 to 5.8 × 10⁷ S/m. The peak values of specific absorption rate (SAR) averaged over different volumes were calculated for each lead conductivity. Experimental measurements were also performed at 3-T MRI with a Gracilaria Lichenoides (GL) phantom with and without a low-conductive EEG lead cap ("InkNet"). The simulation results showed that SAR was a nonlinear function of the EEG lead conductivity. The experimental results were in line with the numerical simulations. Specifically, there was a ΔT of 1.7 °C in the GL phantom without leads compared to ΔT of 1.8 °C calculated with the simulations. Additionally, there was a ΔT of 1.5 °C in the GL phantom with the InkNet compared to a ΔT of 1.7 °C in the simulations with a cap of similar conductivity. The results showed that SAR is affected by specific location, number of electrodes, and the volume of tissue considered. As such, SAR averaged over the whole head, or even SAR averaged over volumes of 1 or 0.1 g, may conceal significant heating effects and local analysis of RF heating (in terms of peak SAR and temperature) is needed.

Keywords: Anatomical models; computational electromagnetic modeling; finite-element method (FEM); specific absorption rate (SAR).

Abstract

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