title: Impact of gradient timing error on the tissue sodium concentration bioscale measured using flexible twisted projection imaging.
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.
authors.affiliation: Center for Magnetic Resonance Research, University of Illinois at Chicago, Chicago, IL 60612, United States. aiminglu@uic.edu
authors.forename: Aiming
authors.initials: A
authors.lastname: Lu
authors.forename: Ian C
authors.initials: IC
authors.lastname: Atkinson
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Vaughn
authors.forename: Keith R
authors.initials: KR
authors.lastname: Thulborn
mesh_terms: D000465:Algorithms; D000818:Animals; D001921:Brain / Q000033:anatomy & histology; D001923:Brain Chemistry; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D011846:Radio Waves; D015203:Reproducibility of Results; D012964:Sodium / Q000032:analysis*; D012975:Sodium Isotopes
chemical_list: D012975:Sodium Isotopes; D012964:Sodium