Effect of Electrical Conductivity Uncertainty in the Assessment of the Electric Fields Induced in the Brain by Exposure to Uniform Magnetic Fields at 50 Hz

Soldati, Marco; Laakso, Ilkka

doi:10.1109/access.2020.3043602

Cited by 13 publications

(10 citation statements)

References 49 publications

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“…After a formal assessment ( Supplementary materials 3 ), we replaced values exceeding the 99.9 th percentile E-field magnitude with the 99.9 th percentile E-field magnitude. This was done as higher values are prone to staircasing errors, and lower values underestimate the peak magnitude [41].…”

Section: Methodsmentioning

confidence: 99%

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

Hoornweder

Nuyts

Frieske

et al. 2023

Preprint

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Background: Electric field (E-field) modeling is a potent tool to examine the cortical effects of transcranial magnetic and electrical stimulation (TMS and tES, respectively) and to address the high variability in efficacy observed in the literature. However, outcome measures used to report E-field magnitude vary considerably and have not yet been compared in detail. Objectives: The goal of this two-part study, encompassing a systematic review and modeling experiment, was to provide an overview of the different outcome measures used to report the magnitude of tES and TMS E-fields, and to conduct a direct comparison of these measures across different stimulation montages. Methods: Three electronic databases were searched for tES and/or TMS studies reporting E-field magnitude. We extracted and discussed outcome measures in studies meeting the inclusion criteria. Additionally, outcome measures were compared via models of four common tES and two TMS modalities in 100 healthy younger adults. Results: In the systematic review, we included 118 studies using 151 outcome measures related to E-field magnitude. Structural and spherical regions of interest (ROI) analyses and percentile-based whole-brain analyses were used most often. In the modeling analyses, we found that there was an average of only 6% overlap between ROI and percentile-based whole-brain analyses in the investigated volumes within the same person. The overlap between ROI and whole-brain percentiles was montage- and person-specific, with more focal montages such as 4x1 and APPS-tES, and figure-of-eight TMS showing up to 73%, 60%, and 52% overlap between ROI and percentile approaches respectively. However, even in these cases, 27% or more of the analyzed volume still differed between outcome measures in every analyses. Conclusions: The choice of outcome measures meaningfully alters the interpretation of tES and TMS E-field models. Well-considered outcome measure selection is imperative for accurate interpretation of results, valid between-study comparisons, and depends on stimulation focality and study goals. We formulated four recommendations to increase the quality and rigor of E-field modeling outcome measures. With these data and recommendations, we hope to guide future studies towards informed outcome measure selection, and improve the comparability of studies.

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Section: Methodsmentioning

confidence: 99%

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

Hoornweder

Nuyts

Frieske

et al. 2023

Preprint

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“…For instance, the conductivity value of the skin can have a large impact on the estimation of the induced electric field [41]. Furthermore, different estimates of brain tissue conductivity can produce discrepancies of approximately one-third in the highest electric field values in the brain [42].…”

Section: A Low-frequency Dosimetrymentioning

confidence: 99%

Assessment of Human Exposure to Electromagnetic Fields: Review and Future Directions

Hirata

Diao

Onishi

et al. 2021

IEEE Trans. Electromagn. Compat.

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This paper reviews recent standardization activities and scientific studies related to the assessment of human exposure to electromagnetic fields (EMF). The differences of human exposure standards and assessment of consumer products and medical applications are summarized. First, we reviewed human body modeling and tissue dielectric properties. Then, we explain the rationale of current exposure standards from the viewpoint of EMF and the standardization process for product compliance based on these exposure standards. The assessment of wireless power transfer, as an example of emerging wireless devices, and environmental EMFs in our daily lives are reviewed. Safety in magnetic resonance systems, where the EMF exposure is much larger than from typical consumer devices, is also reviewed. Finally, we summarize future research directions and research needs for EMF safety.

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“…Several computational electromagnetic methods for analyzing the volume conductor have been used including finite difference, finite element or boundary element methods to solve forward problems. Even using conformal surface modeling (Soldati andLaakso 2020, Conchin et al 2022), this issue inherent to the assignment of tissue-specific conductivity cannot be resolved. Volume conductor modeling and its solution are reciprocal for stimulation and source localization (Dmochowski et al 2017), in addition that the modeling is used for human protection from electromagnetic fields (Reilly and Hirata 2016).…”

Section: Introductionmentioning

confidence: 99%

High-resolution EEG source localization in personalized segmentation-free head model with multi-dipole fitting

Hirata,

Niitsu,

Phang

et al. 2024

Phys. Med. Biol.

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Objective. Electroencephalograms (EEGs) are often used to monitor brain activity. Several source localization methods have been proposed to estimate the location of brain activity corresponding to EEG readings. However, only a few studies evaluated source localization accuracy from measured EEG using personalized head models in a millimeter resolution. In this study, based on a volume conductor analysis of a high-resolution personalized human head model constructed from magnetic resonance images, a finite difference method was used to solve the forward problem and to reconstruct the field distribution. Approach. We used a personalized segmentation-free head model developed using machine learning techniques, in which the abrupt change of electrical conductivity occurred at the tissue interface is suppressed. Using this model, a smooth field distribution was obtained to address the forward problem. Next, multi-dipole fitting was conducted using EEG measurements for each subject (N = 10 male subjects, age: 22.5 ± 0.5), and the source location and electric field distribution were estimated. Main results. For measured somatosensory evoked potential for electrostimulation to the wrist, a multi-dipole model with lead field matrix computed with the volume conductor model was superior than a single dipole model when using personalized segmentation-free models (6/10). The correlation coefficient between measured and estimated scalp potentials was 0.89 for segmentation-free head models and 0.71 for conventional segmented models. The proposed method is straightforward model development and comparable localization difference of the maximum electric field from the target wrist reported using fMR (i.e., 16.4 ± 5.2 mm) in previous study. For comparison, DUNEuro based on sLORETA was (EEG: 17.0±4.0 mm). Significance. For measured EEG signals, our procedures using personalized head models demonstrated that effective localization of the somatosensory cortex, which is located in a non-shallower cortex region. This method may be potentially applied for imaging brain activity located in other non-shallow regions.

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Effect of Electrical Conductivity Uncertainty in the Assessment of the Electric Fields Induced in the Brain by Exposure to Uniform Magnetic Fields at 50 Hz

Cited by 13 publications

References 49 publications

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

Assessment of Human Exposure to Electromagnetic Fields: Review and Future Directions

High-resolution EEG source localization in personalized segmentation-free head model with multi-dipole fitting

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