A multi-scale computational approach based on TMS experiments for the assessment of electro-stimulation thresholds of the brain at intermediate frequencies

Soldati, Marco; Mikkonen, Marko; Laakso, Ilkka; Murakami, Takenobu; Ugawa, Yoshikazu; Hirata, Akimasa

doi:10.1088/1361-6560/aae932

Cited by 21 publications

(17 citation statements)

References 62 publications

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“…A previous study of dose to brain tissue from transcranial magnetic stimulation reported good agreement between the median in situ electric fields and corresponding 95% confidence intervals for both the 2-mm cubic and 5-mm linear averages of in situ electric fields [43]. The study in this paper reports a similar tendency (Table 3) for the ≤ 99.99 th percentile of inner tissues, with relatively large differences for maximum values (100 th percentile).…”

Section: Discussion and Concluding Remarkssupporting

confidence: 81%

Spatial Averaging Schemes of In Situ Electric Field for Low-Frequency Magnetic Field Exposures

et al. 2019

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ICNIRP and IEEE publish standards/guidelines for exposures to low-frequency electromagnetic fields and their associated in situ electric fields. Two methods are prescribed for spatially averaging the in situ electric field to evaluate compliance: averaging (1) over a 2 mm × 2 mm × 2 mm volume (ICNIRP) and (2) along a 5 mm linear segment of neural tissue (IEEE). However, detailed calculation procedures for these two schemes are not provided, particularly when the averaging volume/line straddles a tissue/air or tissue/tissue interface. This study proposes detailed schemes for implementing the volume-and lineaveraging in such cases, applying them to both a spherical model of layered tissues and a human anatomical model. To extend the applicability of the proposed averaging schemes to the voxels at the tissue boundaries, a parameter, p max , is introduced and defined as the maximum permissible percentage of air/other tissues in the averaging volume/line. For most inner-tissue voxels results show good agreement between the two averaging schemes, in general. Excluding skin, the relative differences between the two averaging schemes were less than 9% for the 99 th percentile in situ electric field, and these differences decrease as p max increases. Results indicate that around 20-30% inclusion of air or other tissues for volume averaging of internal tissues provides stable percentile values; less stability is observed across p max for linear averaging. Invoking the suggestion of ICNIRP (2010) that the averaging cube for skin ''may extend to subcutaneous tissue,'' ≥10% inclusion of air results in stable averaged induced electric fields.

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Section: Discussion and Concluding Remarkssupporting

confidence: 81%

Spatial Averaging Schemes of In Situ Electric Field for Low-Frequency Magnetic Field Exposures

et al. 2019

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“…The derived reference level in Fig. 4 showed that allowable external magnetic field strength and in-situ EF established by both guidelines/standards are significantly lower than the internal EF needed for the stimulation of the central nervous system for medical applications [16].…”

Section: Discussionmentioning

confidence: 97%

Setting Reference Level in Human Safety Guidelines via Cortical Nerve Activation Intercomparison at IF

Gómez-Tames

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Hirata

et al. 2019

2019 Joint International Symposium on Electromagnetic Compatibility, Sapporo and Asia-Pacific International Symposium on Electr

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International guidelines/standards have been published for human protection from electromagnetic field exposure. The research in the intermediate frequencies is scattered unlike for other frequencies, and thus the limit prescribed in the guidelines/standards are different by a factor of 10. The IEEE International Committee on Electromagnetic Safety has published a research agenda for exploring the electrostimulation thresholds. However, the consistency of the excitation models for specific target tissue needs to be revised. For this purpose, we present the first intercomparison study using multiphysics modelling to investigate stimulation thresholds during transcranial magnetic stimulation (TMS). To define the stimulation threshold, a non-invasive technique for brain stimulation has been used. In this study, by incorporating individual neurons into electromagnetic computation in realistic head models, stimulation thresholds can be determined. Then, we demonstrated that the allowable external magnetic field strength in the current guidelines/standard is conservative.

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“…Technical Committee 95., Institute of Electrical and Electronics Engineers. and IEEE-SA Standards Board., no date; ICNIRP, 2010), as shown by (Soldati et al, 2018;Gomez-Tames et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

Review on biophysical modelling and simulation studies for transcranial magnetic stimulation

2020

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Transcranial magnetic stimulation (TMS) is a technique for noninvasively stimulating a brain area for therapeutic, rehabilitation treatments and neuroscience research. Despite our understanding of the physical principles and experimental developments pertaining to TMS, it is difficult to identify the exact brain target as the generated dosage exhibits a non-uniform distribution owing to the complicated and subject-dependent brain anatomy and the lack of biomarkers that can quantify the effects of TMS in most cortical areas. Computational dosimetry has progressed significantly and enables TMS assessment by computation of the induced electric field (the primary physical agent known to activate the brain neurons) in a digital representation of the human head. In this review, TMS dosimetry studies are summarised, clarifying the importance of the anatomical and human biophysical parameters and computational methods. This review shows that there is a high consensus on the importance of a detailed cortical folding representation and an accurate modelling of the surrounding cerebrospinal fluid. Recent studies have also enabled the prediction of individually optimised stimulation based on magnetic resonance imaging of the patient/subject and have attempted to understand the temporal effects of TMS at the cellular level by incorporating neural modelling. These efforts, together with the fast deployment of personalised TMS computations, will permit the adoption of TMS dosimetry as a standard procedure in clinical procedures.

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A multi-scale computational approach based on TMS experiments for the assessment of electro-stimulation thresholds of the brain at intermediate frequencies

Cited by 21 publications

References 62 publications

Spatial Averaging Schemes of In Situ Electric Field for Low-Frequency Magnetic Field Exposures

Spatial Averaging Schemes of In Situ Electric Field for Low-Frequency Magnetic Field Exposures

Setting Reference Level in Human Safety Guidelines via Cortical Nerve Activation Intercomparison at IF

Review on biophysical modelling and simulation studies for transcranial magnetic stimulation

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