Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz

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Soellradl, M; Strasser, J; Lesch, A; Stollberger, R; Ropele, S; Langkammer, C.
Adaptive slice-specific z-shimming for 2D spoiled gradient-echo sequences.
Magn Reson Med. 2021; 85(2):818-830 Doi: 10.1002/mrm.28468 [OPEN ACCESS]
Web of Science PubMed FullText FullText_MUG

Führende Autor*innen der Med Uni Graz: Söllradl Martin
Co-Autor*innen der Med Uni Graz: Langkammer Christian; Ropele Stefan; Stollberger Rudolf; Strasser Johannes
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Abstract:: To reduce the misbalance between compensation gradients and macroscopic field gradients, we introduce an adaptive slice-specific z-shimming approach for 2D spoiled multi-echo gradient-echoe sequences in combination with modeling of the signal decay. Macroscopic field gradients were estimated for each slice from a fast prescan (15 seconds) and then used to calculate slice-specific compensation moments along the echo train. The coverage of the compensated field gradients was increased by applying three positive and three negative moments. With a forward model, which considered the effect of the slice profile, the z-shim moment, and the field gradient, R 2 ∗ maps were estimated. The method was evaluated in phantom and in vivo measurements at 3 T and compared with a spoiled multi-echo gradient-echo and a global z-shimming approach without slice-specific compensation. The proposed method yielded higher SNR in R 2 ∗ maps due to a broader range of compensated macroscopic field gradients compared with global z-shimming. In global white matter, the mean interquartile range, proxy for SNR, could be decreased to 3.06 s^-1 with the proposed approach, compared with 3.37 s^-1 for global z-shimming and 3.52 s^-1 for uncompensated multi-echo gradient-echo. Adaptive slice-specific compensation gradients between echoes substantially improved the SNR of R 2 ∗ maps, and the signal could also be rephased in anatomical areas, where it has already been completely dephased. © 2020 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.
Find related publications in this database (Keywords): field inhomogeneities; gradient-echo; R-2* relaxometry; T-2* relaxometry; z-shim