Evaluation of Exposure to (Ultra) High Static Magnetic Fields During Activities Around Human MRI Scanners

MAGMA. 2017 Jun;30(3):255-264. doi: 10.1007/s10334-016-0602-z. Epub 2016 Dec 16.

Abstract

Objective: To assess the individual exposure to the static magnetic field (SMF) and the motion-induced time-varying magnetic field (TVMF) generated by activities in an inhomogeneous SMF near high and ultra-high field magnetic resonance imaging (MRI) scanners. The study provides information on the level of exposure to high and ultra-high field MRI scanners during research activities.

Materials and methods: A three-axis Hall magnetometer was used to determine the SMF and TVMF around human 3- and 7-Tesla (T) MRI systems. The 7-T MRI scanner used in this study was passively shielded and the 3-T scanner was actively shielded and both were from the same manufacturer. The results were compared with the exposure restrictions given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).

Results: The recorded exposure was highly variable between individuals, although they followed the same instructions for moving near the scanners. Maximum exposure values of B = 2057 mT and dB/dt = 4347 mT/s for the 3-T scanner and B = 2890 mT, dB/dt = 3900 mT/s for 7 T were recorded. No correlation was found between reporting the MRI-related sensory effects and exceeding the reference values.

Conclusions: According to the results of our single-center study with five subjects, violation of the ICNIRP restrictions for max B in MRI research environments was quite unlikely at 3 and 7 T. Occasions of exceeding the dB/dt limit at 3 and 7 T were almost similar (30% of 60 exposure scenarios) and highly variable among the individuals.

Keywords: Electromagnetic fields; Exposure assessment; Occupational exposure; Static magnetic field; Time-varying field.

MeSH terms

  • Humans
  • Magnetic Fields*
  • Magnetic Resonance Imaging*
  • Magnetometry / methods*
  • Occupational Exposure / analysis*
  • Radiation Exposure / analysis*
  • Radiation Monitoring / methods*
  • Radiology
  • Reproducibility of Results
  • Sensitivity and Specificity