Variation in Reported Human Head Tissue Electrical Conductivity Values

2019 · Unclear · Moderate evidence

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UnclearModerate evidencePaper 1607

Study snapshot

Publicationmanual · 2019

Study typemeta_analysis

Reported directionUnclear

Evidence ratingModerate

Abstract

Variation in Reported Human Head Tissue Electrical Conductivity Values McCann H, Pisano G, Beltrachini L. Variation in Reported Human Head Tissue Electrical Conductivity Values. Brain Topogr. 2019 Sep;32(5):825-858. doi: 10.1007/s10548-019-00710-2. Abstract Electromagnetic source characterisation requires accurate volume conductor models representing head geometry and the electrical conductivity field. Head tissue conductivity is often assumed from previous literature, however, despite extensive research, measurements are inconsistent. A meta-analysis of reported human head electrical conductivity values was therefore conducted to determine significant variation and subsequent influential factors. Of 3121 identified publications spanning three databases, 56 papers were included in data extraction. Conductivity values were categorised according to tissue type, and recorded alongside methodology, measurement condition, current frequency, tissue temperature, participant pathology and age. We found variation in electrical conductivity of the whole-skull, the spongiform layer of the skull, isotropic, perpendicularly- and parallelly-oriented white matter (WM) and the brain-to-skull-conductivity ratio (BSCR) could be significantly attributed to a combination of differences in methodology and demographics. This large variation should be acknowledged, and care should be taken when creating volume conductor models, ideally constructing them on an individual basis, rather than assuming them from the literature. When personalised models are unavailable, it is suggested weighted average means from the current meta-analysis are used. Assigning conductivity as: 0.41 S/m for the scalp, 0.02 S/m for the whole skull, or when better modelled as a three-layer skull 0.048 S/m for the spongiform layer, 0.007 S/m for the inner compact and 0.005 S/m for the outer compact, as well as 1.71 S/m for the CSF, 0.47 S/m for the grey matter, 0.22 S/m for WM and 50.4 for the BSCR. Open access paper: ncbi.nlm.nih.gov

Machine Enhanced Logic

AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typemeta_analysis

Effect directionunclear

PopulationHumans (head tissue conductivity values from published studies)

Sample size56

ExposureNot supplied

Evidence strengthModerateConfidence: 78% · Peer reviewed: yes

Main findings

A meta-analysis of reported human head tissue electrical conductivity values found substantial variation across studies. Variation in conductivity for several tissues (including whole skull, spongiform skull layer, white matter orientations, and BSCR) could be significantly attributed to combinations of methodological differences and demographics. The authors recommend acknowledging this variation and using individualized volume conductor models when possible; otherwise, weighted average conductivity values from the meta-analysis are suggested.

Outcomes measured

Reported electrical conductivity values of human head tissues (e.g., scalp, skull layers, CSF, grey matter, white matter)
Variation in conductivity values and influential factors (methodology, demographics, measurement conditions)
Brain-to-skull conductivity ratio (BSCR)

View raw extracted JSON

{
  "study_type": "meta_analysis",
  "exposure": {
    "band": null,
    "source": null,
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": "Humans (head tissue conductivity values from published studies)",
  "sample_size": 56,
  "outcomes": [
    "Reported electrical conductivity values of human head tissues (e.g., scalp, skull layers, CSF, grey matter, white matter)",
    "Variation in conductivity values and influential factors (methodology, demographics, measurement conditions)",
    "Brain-to-skull conductivity ratio (BSCR)"
  ],
  "main_findings": "A meta-analysis of reported human head tissue electrical conductivity values found substantial variation across studies. Variation in conductivity for several tissues (including whole skull, spongiform skull layer, white matter orientations, and BSCR) could be significantly attributed to combinations of methodological differences and demographics. The authors recommend acknowledging this variation and using individualized volume conductor models when possible; otherwise, weighted average conductivity values from the meta-analysis are suggested.",
  "effect_direction": "unclear",
  "limitations": [],
  "evidence_strength": "moderate",
  "confidence": 0.78,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "electrical conductivity",
    "head tissues",
    "volume conductor model",
    "skull",
    "white matter",
    "grey matter",
    "CSF",
    "brain-to-skull conductivity ratio",
    "meta-analysis"
  ],
  "suggested_hubs": []
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1007/s10548-019-00710-2
PubMed: Not supplied

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