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

30 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

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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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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

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T1 - Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils

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

Y1 - 2011

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.

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KW - magnetically shielded room

KW - multipole expansion

KW - polarizing coil

KW - ultra-low-field MRI

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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 -