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Conductive shield f...
Conductive shield for ultra-low-field magnetic resonance imaging: Theory and measurements of eddy currents
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- Zevenhoven, Koos C J (author)
- Aalto-Yliopisto,Aalto University,University of California
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- Busch, S. (author)
- University of California,NASA Goddard Space Flight Center
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- Hatridge, M. (author)
- University of California,Yale University
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- Öisjöen, Fredrik, 1982 (author)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Ilmoniemi, Risto J. (author)
- Aalto-Yliopisto,Aalto University
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- Clarke, John, 1942 (author)
- University of California
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(creator_code:org_t)
- AIP Publishing, 2014
- 2014
- English.
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:10, s. 12-
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Abstract
Subject headings
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- Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field-applied before each signal acquisition sequence to increase the signal-induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures. (C) 2014 AIP Publishing LLC.
Subject headings
- NATURVETENSKAP -- Fysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences (hsv//eng)
Keyword
- MRI
Publication and Content Type
- art (subject category)
- ref (subject category)
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