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Soellradl, M; Lesch, A; Strasser, J; Pirpamer, L; Stollberger, R; Ropele, S; Langkammer, C.
Assessment and correction of macroscopic field variations in 2D spoiled gradient-echo sequences.
Magn Reson Med. 2020; 84(2):620-633 Doi: 10.1002/mrm.28139 [OPEN ACCESS]
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Führende Autor*innen der Med Uni Graz
Söllradl Martin
Co-Autor*innen der Med Uni Graz
Langkammer Christian
Pirpamer Lukas
Ropele Stefan
Stollberger Rudolf
Strasser Johannes
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Abstract:
To model and correct the dephasing effects in the gradient-echo signal for arbitrary RF excitation pulses with large flip angles in the presence of macroscopic field variations. The dephasing of the spoiled 2D gradient-echo signal was modeled using a numerical solution of the Bloch equations to calculate the magnitude and phase of the transverse magnetization across the slice profile. Additionally, regional variations of the transmit RF field and slice profile scaling due to macroscopic field gradients were included. Simulations, phantom, and in vivo measurements at 3 T were conducted for R 2 ∗ and myelin water fraction (MWF) mapping. The influence of macroscopic field gradients on R 2 ∗ and myelin water fraction estimation can be substantially reduced by applying the proposed model. Moreover, it was shown that the dephasing over time for flip angles of 60° or greater also depends on the polarity of the slice-selection gradient because of phase variation along the slice profile. Substantial improvements in R 2 ∗ accuracy and myelin water fraction mapping coverage can be achieved using the proposed model if higher flip angles are required. In this context, we demonstrated that the phase along the slice profile and the polarity of the slice-selection gradient are essential for proper modeling of the gradient-echo signal in the presence of macroscopic field variations. © 2019 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Find related publications in this database (Keywords)
field inhomogeneities
myelin water fraction
R-2*
relaxometry
slice profile
T-2*
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