The magnetic artifacts derived from dental metals in magnetoencephalography

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  • Maezawa Hitoshi
    Human Brain Research Center, Graduate School of Medicine, Kyoto University Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kyoto University
  • Matsuhashi Masao
    Human Brain Research Center, Graduate School of Medicine, Kyoto University
  • Yoshida Kazuya
    Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kyoto University Department of Oral and Maxillofacial Surgery, National Hospital Organization, Kyoto Medical Center
  • Sawamoto Nobukatsu
    Human Brain Research Center, Graduate School of Medicine, Kyoto University
  • Mima Tatsuya
    Human Brain Research Center, Graduate School of Medicine, Kyoto University
  • Nagamine Takashi
    Department of System Neuroscience, School of Medicine, Sapporo Medical University
  • Bessho Kazuhisa
    Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kyoto University
  • Fukuyama Hidenao
    Human Brain Research Center, Graduate School of Medicine, Kyoto University

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Other Title
  • 脳磁図計測における歯科用金属に由来するアーチファクト
  • ノウジズ ケイソク ニ オケル シカ ヨウキンゾク ニ ユライ スル アーチファクト

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Abstract

  Magnetoencephalography (MEG) provides an effective non-invasive approach to study human brain function. However, despite the fact that subjects wearing dental metals often encounter troubles due to magnetic artifacts in MEG measurement, little is known about the causal relationship. This study was designed to check magnetic artifacts from dental metals of various compositions when they were used in the conventional MEG measurement settings, focusing on the effect of Magnetic Resonance Imaging (MRI) scan. We collected eighteen kinds of dental metals commonly used in daily practice, including eight metals mainly made up of ferromagnetic substance. We measured the magnetic fields using a whole head MEG system in the following four conditions;1. unprocessed, 2. after demagnetization, 3. after MRI scanning, 4. after second demagnetization. Each sample made regular reciprocal movement driven by a shaker machine placed outside a magnetically shielded room and the magnetic fields from the sample were measured for one minute. One minute recording with a shaker running without a sample was made 10 times as control in each condition. A sample was judged as a source of magnetic artifacts when the mean power of the magnetic fields exceeded average plus 5 times standard deviation of that of the control data. In 8 types of ferromagnetic-based dental metals, 6, 5, 8 and 7 types caused artifacts in the four conditions, respectively. In 10 types of non-ferromagnetic dental metals, 1, 0, 4 and 2 types caused artifacts in the four conditions, respectively. These results indicate that any dental metal can become magnetized during MRI recording regardless of whether it contains ferromagnetic metal or not, although the magnitude of magnetic artifacts depends on its element compositions. This conclusion should be taken into consideration in MEG recording dealing with subjects wearing various dental metals.

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