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Optimization of pseudo‐continuous arterial spin labeling at 7T with parallel transmission B1 shimming
Author(s) -
Wang Kai,
Ma Samantha J.,
Shao Xingfeng,
Zhao Chenyang,
Shou Qinyang,
Yan Lirong,
Wang Danny J. J.
Publication year - 2022
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28988
Subject(s) - shim (computing) , intraclass correlation , nuclear medicine , repeatability , nuclear magnetic resonance , biomedical engineering , perfusion , materials science , physics , medicine , mathematics , reproducibility , surgery , radiology , erectile dysfunction , statistics
Purpose To optimize pseudo‐continuous arterial spin labeling (pCASL) for 7 T, and to further improve the labeling efficiency with parallel RF transmission transmit B 1 ( B 1 + ) shimming. Methods pCASL parameters were optimized based onB 1 + / B 0field distributions at 7 T with simulation. To increase labeling efficiency, the B 1 + amplitude at inflowing arteries was increased with parallel RF transmission B 1 + shimming. The “indv‐shim” with shimming weights calculated for each individual subject, and the “univ‐shim” with universal weights calculated on a group of 12 subjects, were compared with circular polarized (CP) shim. The optimized pCASL sequences with three B 1 + shimming modes (indv‐shim, univ‐shim, and CP‐shim) were evaluated in 6 subjects who underwent two repeated scans 24 hours apart, along with a pulsed ASL sequence. Quantitative metrics including mean B 1 + amplitude, perfusion, and intraclass correlation coefficient were calculated. The optimized 7T pCASL was compared with standard 3T pCASL on 5 subjects, using spatial SNR and temporal SNR. Results The optimal pCASL parameter set (RF duration/gap = 300/250 us,G ave = 0.6 mT / m , g R a t i o = 10 ) achieved robust perfusion measurement in the presence ofB 1 + / B 0inhomogeneities. Both indv‐shim and univ‐shim significantly increased B 1 + amplitude compared with CP‐shim in simulation and in vivo experiment ( P < .01). Compared with CP‐shim, perfusion signal was increased by 9.5% with indv‐shim ( P < .05) and by 5.3% with univ‐shim ( P = .35). All three pCASL sequences achieved fair to good repeatability (intraclass correlation coefficient ≥ 0.5). Compared with 3T pCASL, the optimized 7T pCASL achieved 78.3% higher spatial SNR and 200% higher temporal SNR. Conclusion The optimized pCASL achieved robust perfusion imaging at 7 T, while both indv‐shim and univ‐shim further increased labeling efficiency.