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ID 30278
FullText URL
Author
Suenaga, Ryousuke
Miyata, Koji
Ohashi, Ken
Abstract

Summary form only given. The flux distribution of a permanent magnet type of MRI shown in Fig.1 is affected by the hysteresis (minor loop) and eddy currents in the pole piece and yoke due to the pulse current (Fig.2) of the gradient coil. In this paper, the effects of the hysteresis and the eddy current in the yoke on the residual flux density of the probe coil are investigated. It can be assumed that the eddy current does not flow in the pole piece because it is divided into pieces. The eddy current flows in the yoke. Fig.3 shows the change of residual flux density /spl Delta/B/sub z/ at the point S(0,0) in Fig.1. /spl Delta/B/sub z/ is given by /spl Delta/B/sub z/=B/sub z1/-B/sub z0/ (1), where B/sub z0/ is the flux density at the instant t=0(I=0A). B/sub z1/ is the flux density at the instant t=i(I=0A). The instant of 1,2,3,... in Fig.2 corresponds to 1,2,3,... in Fig.3. Fig.3 shows that the hysteresis in the pole piece and yoke should be taken into account. The effect of eddy current in the yoke on the residual flux density /spl Delta/B/sub z/ is not negligible. These results suggests that the reduction of the amplitudes of minor loop and eddy current is important in order to improve the operating characteristics of the permanent magnet type of MRI.

Keywords
eddy currents
magnetic flux
magnetic hysteresis
magnetic resonance imaging
permanent magnets
Note
Digital Object Identifier:10.1109/INTMAG.2002.1001224
Published with permission from the copyright holder. This is the institute's copy, as published in Magnetics Conference, 2002. INTERMAG Europe 2002. Digest of Technical Papers. 2002 IEEE International, 28 April-2 May 2006, Pages EV2.
Publisher URL:http://dx.doi.org/10.1109/INTMAG.2002.1001224
Copyright © 2002 IEEE. All rights reserved.
Published Date
2006-5
Publication Title
Magnetics Conference
Content Type
Journal Article
language
英語
Refereed
True
DOI
Submission Path
electricity_and_magnetism/96