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Rapid in vivo proton shimming
Author(s) -
Schneider Erika,
Glover Gary
Publication year - 1991
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.1910180208
Subject(s) - shim (computing) , homogeneity (statistics) , flip angle , nuclear magnetic resonance , pulse sequence , gradient echo , in vivo , spectroscopy , materials science , optics , physics , computer science , magnetic resonance imaging , biology , radiology , machine learning , medicine , microbiology and biotechnology , quantum mechanics , erectile dysfunction
A rapid and completely automated method of adjusting the magnetic field ( B 0 ) homogeneity for in vivo proton spectroscopy and imaging is described. Bo inhomogeneity maps are generated by a gradient‐recalled echo pulse sequence in which the frequency dispersion is chosen to eliminate the effects of the fat/water chemical shift. Low‐order shim values are derived by magnitude‐weighted least‐squares fits to the B 0 maps and automatically applied as DC offsets to the X, Y , and Z gradient amplifiers. Imaging with chemical shift selective saturation is used as a measure of the efficacy of the technique. Results indicate that AUTOSHIM improves the overall homogeneity; however, local high‐order field distortions which cannot be corrected by linear gradients are generated by certain air/tissue and bone/tissue morphology. In such cases a “ZOOM SHIM” may be applied over a limited region of interest for local homogeneity improvement at the expense of other regions. It is suggested that such scans are a necessity for recording the homogeneity during clinical MR spectroscopy. © 1991 Academic Press. Inc.