Characterization of open issues in low-frequency computational dosimetry

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Journal ISSN
Volume Title
School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2021-06-11
Date
2021
Major/Subject
Mcode
Degree programme
Language
en
Pages
93 + app. 77
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 74/2021
Abstract
Two international organizations, namely the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers International Committee on Electromagnetic Safety (IEEE ICES), have established exposure criteria and safety limits for human protection to electromagnetic fields. In the low-frequency range, both organizations recognize that the main adverse health effects are represented by the induction of retinal phosphenes, the alteration of synaptic activity and the stimulation of nerves. On this basis, the exposure limits were derived from threshold data of internal electric fields with the purpose of avoiding such adverse effects. Since direct measurement of the induced electric field is not feasible, both the standard and guidelines have introduced limits for external electric and magnetic field strengths. In this context, computational dosimetry was used to relate the internal induced quantities with the external field strengths. However, low-frequency dosimetry suffers from various sources of error and uncertainty.The main aim of the present thesis is to lessen such uncertainty, as well as further characterize computational artifacts in the evaluation of the induced electric fields. Investigations were carried out using state-of-the-art methods based on physiological measurements, high-resolution realistic anatomical models, individualized electric field computations and biological axon models. Several open issues affecting low-frequency dosimetry have been characterized with the aim of producing quantitative data useful for the harmonization and revision of current exposure standard and guidelines. Our findings showed a large margin of safety in the current exposure limits established by both international organizations. In this regard, the obtained results represent a solid basis for deriving safety levels that offer acceptable protection for the human population without being overly conservative. In addition, the present work improves the reliability of human exposure assessment at low frequencies.
Description
Defence is held on 11.6.2021 12:00 – 15:00 https://aalto.zoom.us/j/61163441113
Supervising professor
Laakso, Ilkka, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland
Thesis advisor
Laakso, Ilkka, Prof., Aalto University, Finland
Keywords
non-invasive brain stimulation, transcranial magnetic stimulation, international safety standard/guidelines, low-frequency dosimetry, individualized models, electrostimulation models, finite element method
Other note
Parts
  • [Publication 1]: Marco Soldati, Marko Mikkonen, Ilkka Laakso, Takenobu Murakami, Yoshikazu Ugawa and Akimasa Hirata. A multi-scale computational approach based on TMS experiments for the assessment of electro- stimulation thresholds of the brain at intermediate frequencies. Accepted for publication in Physics in Medicine & Biology, 63 (22), 225006, November 2018.
    DOI: 10.1088/1361-6560/aae932 View at publisher
  • [Publication 2]: Marco Soldati and Ilkka Laakso. Computational errors of the induced electric field in voxelized and tetrahedral anatomical head models exposed to spatially uniform and localized magnetic fields. Accepted for publication in Physics in Medicine & Biology, 65 (1), 015001, January 2020.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202103222496
    DOI: 10.1088/1361-6560/ab5dfb View at publisher
  • [Publication 3]: Marco Soldati, Takenobu Murakami and Ilkka Laakso. Inter-individual variations in electric fields induced in the brain by exposure to uniform magnetic fields at 50 Hz. Accepted for publication in Physics in Medicine & Biology, 65 (21), 215006, October 2020.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202103222452
    DOI: 10.1088/1361-6560/aba21e View at publisher
  • [Publication 4]: Marco Soldati and Ilkka Laakso. 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. Accepted for publication in IEEE Access, 8, 222297–222309, December 2020.
    DOI: 10.1109/ACCESS.2020.3043602 View at publisher
Citation