Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils

J.O. Nieminen (Corresponding Author), P.T. Vesanen, K.C.J. Zevenhoven, J. Dabek, Juha Hassel, Juho Luomahaara, J.S. Penttilä, R.J. Ilmoniemi

    Research output: Contribution to journalArticleScientificpeer-review

    31 Citations (Scopus)

    Abstract

    In ultra-low-field magnetic resonance imaging (ULF MRI), superconductive sensors are used to detect MRI signals typically in fields on the order of 10–100 μT. Despite the highly sensitive detectors, it is necessary to prepolarize the sample in a stronger magnetic field on the order of 10–100 mT, which has to be switched off rapidly in a few milliseconds before signal acquisition. In addition, external magnetic interference is commonly reduced by situating the ULF-MRI system inside a magnetically shielded room (MSR). With typical dipolar polarizing coil designs, the stray field induces strong eddy currents in the conductive layers of the MSR. These eddy currents cause significant secondary magnetic fields that may distort the spin dynamics of the sample, exceed the dynamic range of the sensors, and prevent simultaneous magnetoencephalography and MRI acquisitions. In this paper, we describe a method to design self-shielded polarizing coils for ULF MRI. The experimental results show that with a simple self-shielded polarizing coil, the magnetic fields caused by the eddy currents are largely reduced. With the presented shielding technique, ULF-MRI devices can utilize stronger and spatially broader polarizing fields than achievable with unshielded polarizing coils.
    Original languageEnglish
    Pages (from-to)154-160
    Number of pages7
    JournalJournal of Magnetic Resonance
    Volume212
    Issue number1
    DOIs
    Publication statusPublished - 2011
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    eddy currents
    coils
    rooms
    magnetic resonance
    acquisition
    magnetic fields
    sensors
    spin dynamics
    dynamic range
    shielding
    interference
    causes
    detectors

    Keywords

    • Eddy currents
    • magnetically shielded room
    • multipole expansion
    • polarizing coil
    • ultra-low-field MRI

    Cite this

    Nieminen, J. O., Vesanen, P. T., Zevenhoven, K. C. J., Dabek, J., Hassel, J., Luomahaara, J., ... Ilmoniemi, R. J. (2011). Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils. Journal of Magnetic Resonance, 212(1), 154-160. https://doi.org/10.1016/j.jmr.2011.06.022
    Nieminen, J.O. ; Vesanen, P.T. ; Zevenhoven, K.C.J. ; Dabek, J. ; Hassel, Juha ; Luomahaara, Juho ; Penttilä, J.S. ; Ilmoniemi, R.J. / Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils. In: Journal of Magnetic Resonance. 2011 ; Vol. 212, No. 1. pp. 154-160.
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    abstract = "In ultra-low-field magnetic resonance imaging (ULF MRI), superconductive sensors are used to detect MRI signals typically in fields on the order of 10–100 μT. Despite the highly sensitive detectors, it is necessary to prepolarize the sample in a stronger magnetic field on the order of 10–100 mT, which has to be switched off rapidly in a few milliseconds before signal acquisition. In addition, external magnetic interference is commonly reduced by situating the ULF-MRI system inside a magnetically shielded room (MSR). With typical dipolar polarizing coil designs, the stray field induces strong eddy currents in the conductive layers of the MSR. These eddy currents cause significant secondary magnetic fields that may distort the spin dynamics of the sample, exceed the dynamic range of the sensors, and prevent simultaneous magnetoencephalography and MRI acquisitions. In this paper, we describe a method to design self-shielded polarizing coils for ULF MRI. The experimental results show that with a simple self-shielded polarizing coil, the magnetic fields caused by the eddy currents are largely reduced. With the presented shielding technique, ULF-MRI devices can utilize stronger and spatially broader polarizing fields than achievable with unshielded polarizing coils.",
    keywords = "Eddy currents, magnetically shielded room, multipole expansion, polarizing coil, ultra-low-field MRI",
    author = "J.O. Nieminen and P.T. Vesanen and K.C.J. Zevenhoven and J. Dabek and Juha Hassel and Juho Luomahaara and J.S. Penttil{\"a} and R.J. Ilmoniemi",
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    Nieminen, JO, Vesanen, PT, Zevenhoven, KCJ, Dabek, J, Hassel, J, Luomahaara, J, Penttilä, JS & Ilmoniemi, RJ 2011, 'Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils', Journal of Magnetic Resonance, vol. 212, no. 1, pp. 154-160. https://doi.org/10.1016/j.jmr.2011.06.022

    Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils. / Nieminen, J.O. (Corresponding Author); Vesanen, P.T.; Zevenhoven, K.C.J.; Dabek, J.; Hassel, Juha; Luomahaara, Juho; Penttilä, J.S.; Ilmoniemi, R.J.

    In: Journal of Magnetic Resonance, Vol. 212, No. 1, 2011, p. 154-160.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

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    AU - Nieminen, J.O.

    AU - Vesanen, P.T.

    AU - Zevenhoven, K.C.J.

    AU - Dabek, J.

    AU - Hassel, Juha

    AU - Luomahaara, Juho

    AU - Penttilä, J.S.

    AU - Ilmoniemi, R.J.

    PY - 2011

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    N2 - In ultra-low-field magnetic resonance imaging (ULF MRI), superconductive sensors are used to detect MRI signals typically in fields on the order of 10–100 μT. Despite the highly sensitive detectors, it is necessary to prepolarize the sample in a stronger magnetic field on the order of 10–100 mT, which has to be switched off rapidly in a few milliseconds before signal acquisition. In addition, external magnetic interference is commonly reduced by situating the ULF-MRI system inside a magnetically shielded room (MSR). With typical dipolar polarizing coil designs, the stray field induces strong eddy currents in the conductive layers of the MSR. These eddy currents cause significant secondary magnetic fields that may distort the spin dynamics of the sample, exceed the dynamic range of the sensors, and prevent simultaneous magnetoencephalography and MRI acquisitions. In this paper, we describe a method to design self-shielded polarizing coils for ULF MRI. The experimental results show that with a simple self-shielded polarizing coil, the magnetic fields caused by the eddy currents are largely reduced. With the presented shielding technique, ULF-MRI devices can utilize stronger and spatially broader polarizing fields than achievable with unshielded polarizing coils.

    AB - In ultra-low-field magnetic resonance imaging (ULF MRI), superconductive sensors are used to detect MRI signals typically in fields on the order of 10–100 μT. Despite the highly sensitive detectors, it is necessary to prepolarize the sample in a stronger magnetic field on the order of 10–100 mT, which has to be switched off rapidly in a few milliseconds before signal acquisition. In addition, external magnetic interference is commonly reduced by situating the ULF-MRI system inside a magnetically shielded room (MSR). With typical dipolar polarizing coil designs, the stray field induces strong eddy currents in the conductive layers of the MSR. These eddy currents cause significant secondary magnetic fields that may distort the spin dynamics of the sample, exceed the dynamic range of the sensors, and prevent simultaneous magnetoencephalography and MRI acquisitions. In this paper, we describe a method to design self-shielded polarizing coils for ULF MRI. The experimental results show that with a simple self-shielded polarizing coil, the magnetic fields caused by the eddy currents are largely reduced. With the presented shielding technique, ULF-MRI devices can utilize stronger and spatially broader polarizing fields than achievable with unshielded polarizing coils.

    KW - Eddy currents

    KW - magnetically shielded room

    KW - multipole expansion

    KW - polarizing coil

    KW - ultra-low-field MRI

    U2 - 10.1016/j.jmr.2011.06.022

    DO - 10.1016/j.jmr.2011.06.022

    M3 - Article

    VL - 212

    SP - 154

    EP - 160

    JO - Journal of Magnetic Resonance

    JF - Journal of Magnetic Resonance

    SN - 1090-7807

    IS - 1

    ER -