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J Magn Reson. 2011 Dec;213(1):176-81. doi: 10.1016/j.jmr.2011.08.036. Epub 2011 Sep 5.

Impact of gradient timing error on the tissue sodium concentration bioscale measured using flexible twisted projection imaging.

Author information

  • 1Center for Magnetic Resonance Research, University of Illinois at Chicago, Chicago, IL 60612, United States. aiminglu@uic.edu

Abstract

The rapid biexponential transverse relaxation of the sodium MR signal from brain tissue requires efficient k-space sampling for quantitative imaging in a time that is acceptable for human subjects. The flexible twisted projection imaging (flexTPI) sequence has been shown to be suitable for quantitative sodium imaging with an ultra-short echo time to minimize signal loss. The fidelity of the k-space center location is affected by the readout gradient timing errors on the three physical axes, which is known to cause image distortion for projection-based acquisitions. This study investigated the impact of these timing errors on the voxel-wise accuracy of the tissue sodium concentration (TSC) bioscale measured with the flexTPI sequence. Our simulations show greater than 20% spatially varying quantification errors when the gradient timing errors are larger than 10 μs on all three axes. The quantification is more tolerant of gradient timing errors on the Z-axis. An existing method was used to measure the gradient timing errors with <1 μs error. The gradient timing error measurement is shown to be RF coil dependent, and timing error differences of up to ∼16 μs have been observed between different RF coils used on the same scanner. The measured timing errors can be corrected prospectively or retrospectively to obtain accurate TSC values.

Copyright © 2011 Elsevier Inc. All rights reserved.

PMID:
21944734
[PubMed - indexed for MEDLINE]
PMCID:
PMC3217314
Free PMC Article

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