Exposure of Infants to Gradient Fields in a Baby MRI Scanner

Bioelectromagnetics · 2022 · Harm · Low evidence

← Research stream

HarmLow evidencePaper 815

Study snapshot

PublicationBioelectromagnetics · 2022

Study typeexposure_assessment

Reported directionHarm

Evidence ratingLow

Abstract

Exposure of Infants to Gradient Fields in a Baby MRI Scanner Fangfang Tang, Luca Giaccone, Jiahao Hao, Fabio Freschi, Tongning Wu, Stuart Crozier, Feng Liu. Exposure of Infants to Gradient Fields in a Baby MRI Scanner. Bioelectromagnetics. 2022 Feb;43(2):69-80. doi: 10.1002/bem.22387. Abstract In pediatric magnetic resonance imaging (MRI), infants are exposed to rapid, time-varying gradient magnetic fields, leading to electric fields induced in the body of infants and potential safety risks (e.g. peripheral nerve stimulation). In this numerical study, the in situ electric fields in infants induced by small-sized gradient coils for a 1.5 T MRI scanner were evaluated. The gradient coil set was specially designed for the efficient imaging of infants within a small-bore (baby) scanner. The magnetic flux density and induced electric fields by the small x, y, z gradient coils in an infant model (8-week-old with a mass of 4.3 kg) were computed using the scalar potential finite differences method. The gradient coils were driven by a 1 kHz sinusoidal waveform and also a trapezoidal waveform with a 250 µs rise time. The model was placed at different scan positions, including the head area (position I), chest area (position II), and body center (position III). It was found that the induced electric fields in most tissues exceeded the basic restrictions of the ICNIRP 2010 guidelines for both waveforms. The electric fields were similar in the region of interest for all coil types and model positions but different outside the imaging region. The y-coil induced larger electric fields compared with the x- and z- coils. pubmed.ncbi.nlm.nih.gov Conclusions In this paper, we have numerically studied the field exposure of an infant model inside the baby x, y, z gradient coils during an MRI scan. The B-fields have exceeded the reference level 0.08 mT in most tissues for the frequency 1 kHz in ICNIRP 2010 guidelines. Based on the simulation results, it has been found that baby positioning primarily affected the induced E-field profiles. In most tissues, the EI values are larger than 1, indicating that the exposures have exceeded the reference level 0.4 V/m in ICNIRP 2010 guidelines for the frequency of 1 kHz. The largest E99.9% and EI are 5.41 V/m and 9.56, found in fat produced by y-coil in position III. The EI is determined based on the basic restrictions of ICNIRP 2010 guidelines; the results are possibly conservative as applicable guidelines/restrictions are not yet accessible for exposure of infants in MRI gradient fields. The field exposure varies due to the variation of the driving current and rise time. It is likely stronger when all three gradient coils are switched faster and simultaneously during a realistic MRI scan. Further work is required to characterize more realistic field-infant tissue interactions with detailed nerve models, and it is hoped that these simulations will help inform compliance of clinical procedures.

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 typeexposure_assessment

Effect directionharm

PopulationInfant model (8-week-old, 4.3 kg) in a 1.5 T baby MRI scanner

Sample sizeNot supplied

ExposureELF

Evidence strengthLowConfidence: 78% · Peer reviewed: yes

Main findings

In numerical simulations of an 8-week-old infant model in a small-bore 1.5 T baby MRI scanner, induced electric fields in most tissues exceeded ICNIRP 2010 guideline limits for 1 kHz for both sinusoidal (1 kHz) and trapezoidal (250 µs rise time) gradient waveforms. The y-gradient coil produced larger induced electric fields than the x- and z-coils, and positioning primarily affected induced E-field profiles; the largest reported E99.9% was 5.41 V/m with EI 9.56 in fat for the y-coil at the body-center position.

Outcomes measured

Computed in situ induced electric fields in infant tissues from x/y/z gradient coils
Comparison of induced fields to ICNIRP 2010 basic restrictions/reference levels (E-field and B-field)
Electric field variation by coil type (x, y, z) and infant scan position (head/chest/body center)
Exposure index (EI) and E99.9% metrics

Limitations

Numerical/simulation study (no direct measurements in infants reported)
Only one infant model described (8-week-old, 4.3 kg)
Results described as possibly conservative; authors note guidelines/restrictions for infant exposure in MRI gradient fields are not yet accessible
Waveforms modeled include 1 kHz sinusoid and trapezoid with 250 µs rise time; realistic MRI sequences with simultaneous switching may differ
Further work suggested with more realistic field–tissue interactions and detailed nerve models

View raw extracted JSON

{
  "study_type": "exposure_assessment",
  "exposure": {
    "band": "ELF",
    "source": "MRI gradient fields (baby MRI scanner)",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": "Infant model (8-week-old, 4.3 kg) in a 1.5 T baby MRI scanner",
  "sample_size": null,
  "outcomes": [
    "Computed in situ induced electric fields in infant tissues from x/y/z gradient coils",
    "Comparison of induced fields to ICNIRP 2010 basic restrictions/reference levels (E-field and B-field)",
    "Electric field variation by coil type (x, y, z) and infant scan position (head/chest/body center)",
    "Exposure index (EI) and E99.9% metrics"
  ],
  "main_findings": "In numerical simulations of an 8-week-old infant model in a small-bore 1.5 T baby MRI scanner, induced electric fields in most tissues exceeded ICNIRP 2010 guideline limits for 1 kHz for both sinusoidal (1 kHz) and trapezoidal (250 µs rise time) gradient waveforms. The y-gradient coil produced larger induced electric fields than the x- and z-coils, and positioning primarily affected induced E-field profiles; the largest reported E99.9% was 5.41 V/m with EI 9.56 in fat for the y-coil at the body-center position.",
  "effect_direction": "harm",
  "limitations": [
    "Numerical/simulation study (no direct measurements in infants reported)",
    "Only one infant model described (8-week-old, 4.3 kg)",
    "Results described as possibly conservative; authors note guidelines/restrictions for infant exposure in MRI gradient fields are not yet accessible",
    "Waveforms modeled include 1 kHz sinusoid and trapezoid with 250 µs rise time; realistic MRI sequences with simultaneous switching may differ",
    "Further work suggested with more realistic field–tissue interactions and detailed nerve models"
  ],
  "evidence_strength": "low",
  "confidence": 0.78,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "infant",
    "pediatric MRI",
    "baby MRI scanner",
    "gradient coils",
    "time-varying magnetic fields",
    "induced electric field",
    "peripheral nerve stimulation",
    "ICNIRP 2010",
    "numerical simulation",
    "1.5 T",
    "1 kHz"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.78,
      "reason": "Study explicitly evaluates exposure relative to ICNIRP 2010 guideline reference levels/basic restrictions."
    },
    {
      "slug": "occupational-exposure",
      "weight": 0,
      "reason": null
    }
  ]
}

AI can be wrong. Always verify against the paper.

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: 10.1002/bem.22387
PubMed: 35005795

Read the original paper →

Related papers

← Back to the Research Library