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Dynamic shim updating (DSU) for multislice signal acquisition
Author(s) -
de Graaf Robin A.,
Brown Peter B.,
McIntyre Scott,
Rothman Douglas L.,
Nixon Terence W.
Publication year - 2003
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10404
Subject(s) - shim (computing) , multislice , homogeneity (statistics) , computer science , nuclear magnetic resonance , physics , machine learning , erectile dysfunction , medicine
Dynamic shim updating (DSU) is a technique for achieving optimal magnetic field homogeneity over extended volumes by dynamically updating an optimal shim setting for each individual slice in a multislice acquisition protocol. Here the practical implementation of DSU using all first‐ and second‐order shims is described. In particular, the hardware modifications and software requirements are demonstrated. Furthermore, the temporal effects of dynamically switching shim currents are investigated and a Z 2 ‐to‐Z 0 compensation unit is described and implemented to counteract the temporal Z 0 variations following a change in the Z 2 shim current. The optimal shim settings for all slices are determined with a quantitative and user‐independent, multislice phase‐mapping sequence. The performance of DSU is evaluated from multislice phase maps and spectroscopic images acquired on rat brain in vivo. DSU improved the magnetic field homogeneity over all spatial slices, with a more pronounced effect on the slices positioned away from the magnet isocenter, thereby making the magnetic field homogeneity highly uniform over an extended volume. Magn Reson Med 49:409–416, 2003. © 2003 Wiley‐Liss, Inc.