TY - JOUR
T1 - Adaptive slice-specific z-shimming for 2D spoiled gradient-echo sequences
AU - Soellradl, Martin
AU - Strasser, Johannes
AU - Lesch, Andreas
AU - Stollberger, Rudolf
AU - Ropele, Stefan
AU - Langkammer, Christian
N1 - © 2020 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.
PY - 2020/9
Y1 - 2020/9
N2 - Purpose: 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. Methods: 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, (Formula presented.) 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. Results: The proposed method yielded higher SNR in (Formula presented.) 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. Conclusion: Adaptive slice-specific compensation gradients between echoes substantially improved the SNR of (Formula presented.) maps, and the signal could also be rephased in anatomical areas, where it has already been completely dephased.
AB - Purpose: 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. Methods: 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, (Formula presented.) 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. Results: The proposed method yielded higher SNR in (Formula presented.) 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. Conclusion: Adaptive slice-specific compensation gradients between echoes substantially improved the SNR of (Formula presented.) maps, and the signal could also be rephased in anatomical areas, where it has already been completely dephased.
KW - field inhomogeneities
KW - gradient-echo
KW - R2∗ relaxometry
KW - T2∗ relaxometry
KW - z-shim
UR - http://www.scopus.com/inward/record.url?scp=85090459972&partnerID=8YFLogxK
U2 - 10.1002/mrm.28468
DO - 10.1002/mrm.28468
M3 - Article
C2 - 32909334
VL - 85
SP - 818
EP - 830
JO - Magnetic Resonance in Medicine
JF - Magnetic Resonance in Medicine
SN - 0740-3194
IS - 2
ER -