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Technical Note
Slice offset frequency and shim adjustment for interactive steady-state free-precession (SSFP) imaging
Article first published online: 22 APR 2009
DOI: 10.1002/jmri.21752
Copyright © 2009 Wiley-Liss, Inc.
Additional Information
How to Cite
Graves, M. J., Wong, P., Priest, A. N., Black, R. T. and Lomas, D. J. (2009), Slice offset frequency and shim adjustment for interactive steady-state free-precession (SSFP) imaging. J. Magn. Reson. Imaging, 29: 1230–1233. doi: 10.1002/jmri.21752
Publication History
- Issue published online: 22 APR 2009
- Article first published online: 22 APR 2009
- Manuscript Accepted: 5 FEB 2009
- Manuscript Received: 24 OCT 2008
Funded by
- National Institute for Health Research Comprehensive Biomedical Research Centre Award, Department of Health
- Abstract
- Article
- References
- Cited By
Keywords:
- artifacts;
- interactive imaging;
- steady-state free-precession;
- dynamic center frequency;
- dynamic shimming
Abstract
Purpose
To devise a method allowing real-time optimization of center frequency (CF) and shim for an interactive steady-state free-precession (SSFP) sequence by reformatting a previously acquired field map in the same orientation as the interactive acquisition.
Materials and Methods
Field maps were acquired in a rectangular parallel-piped phantom and a normal volunteer. An SSFP sequence was modified to communicate the current slice offset and rotation to an external program that reformatted the field map into the same plane, calculated the CF and shim offsets, and passed them back to the sequence. CF offsets as a function of position for the phantom were compared with the scanner prescan-determined offset.
Results
In the phantom, the CF measurements agreed with the scanner-determined offsets. Bland-Altman analysis showed a bias of −14 Hz (field map – prescan) and limits of agreement of −28 to 0 Hz. In the volunteer there was a qualitative improvement in image quality when using the optimized center frequencies and shims.
Conclusion
The proposed method demonstrates how CF and shim can be optimized for any interactively positioned slice, resulting in reduced off-resonance artifacts. J. Magn. Reson. Imaging 2009;29:1230–1233. © 2009 Wiley-Liss, Inc.