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Robust automated shimming technique using arbitrary mapping acquisition parameters (RASTAMAP)
Author(s) -
Klassen L. Martyn,
Me Ravi S.
Publication year - 2004
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.20094
Subject(s) - shim (computing) , imaging phantom , homogeneity (statistics) , electromagnetic coil , eddy current , computer science , magnetic field , nuclear magnetic resonance , asymmetry , flip angle , physics , acoustics , optics , magnetic resonance imaging , medicine , quantum mechanics , machine learning , erectile dysfunction , radiology
Quantitative MRI techniques as well as methods such as blood oxygen level‐dependent (BOLD) imaging and in vivo spectroscopy require stringent optimization of magnetic field homogeneity, particularly when using high main magnetic fields. Automated shimming approaches require a method of measuring the main magnetic field, B 0 , followed by adjusting the currents in resistive shim coils to maximize homogeneity. A r obust a utomated s himming t echnique using a rbitrary m apping a cquisition p arameters (RASTAMAP) using a 3D multiecho gradient echo sequence that measures B 0 with high precision was developed. Inherent compensation and postprocessing methods enable removal of artifacts due to hardware timing errors, gradient propagation delays, gradient amplifier asymmetry, and eddy currents. This allows field maps to be generated for any field of view, bandwidth, resolution, or acquisition orientation without custom tuning of sequence parameters. Field maps of an aqueous phantom show ± 1 Hz variation with altered acquisition orientations and bandwidths. Subsequent fitting of measured shim coil field maps allows calculation of shim currents to produce optimum field homogeneity. Magn Reson Med 51:881–887, 2004. © 2004 Wiley‐Liss, Inc.