Localization errors in MR spectroscopic imaging due to the drift of the main magnetic field and their correction
Article first published online: 19 NOV 2012
Copyright © 2012 Wiley Periodicals, Inc.
Magnetic Resonance in Medicine
Volume 70, Issue 4, pages 895–904, October 2013
How to Cite
Tal, A. and Gonen, O. (2013), Localization errors in MR spectroscopic imaging due to the drift of the main magnetic field and their correction. Magn Reson Med, 70: 895–904. doi: 10.1002/mrm.24536
- Issue published online: 24 SEP 2013
- Article first published online: 19 NOV 2012
- Manuscript Revised: 1 OCT 2012
- Manuscript Accepted: 1 OCT 2012
- Manuscript Received: 8 AUG 2012
- NIH. Grant Numbers: NS050520, EB01015
- Human Frontiers Science Project
- B0 drift;
- field instabilities;
- chemical shift imaging;
- localization errors
Purpose: To analyze the effect of B0 field drift on multivoxel MR spectroscopic imaging and to propose an approach for its correction.
Theory and Methods: It is shown, both theoretically and in a phantom, that for ∼30 min acquisitions a linear B0 drift (∼0.1 ppm/h) will cause localization errors that can reach several voxels (centimeters) in the slower varying phase encoding directions. An efficient and unbiased estimator is proposed for tracking the drift by interleaving short (∼ ), nonlocalized acquisitions on the nonsuppressed water each pulse repetition time, as shown in 10 volunteers at 1.5 and 3 T.
Results: The drift is shown to be predominantly linear in both the phantom and volunteers at both fields. The localization errors are observed and quantified in both phantom and volunteers. The unbiased estimator is shown to reliably track the instantaneous frequency in vivo despite only using a small portion of the FID.
Conclusion: Contrary to single-voxel MR spectroscopy, where it leads to line broadening, field drift can lead to localization errors in the longer chemical shift imaging experiments. Fortunately, this drift can be obtained at a negligible cost to sequence timing, and corrected for in post processing. Magn Reson Med, 70:895–904, 2013. © 2012 Wiley Periodicals, Inc.