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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.

Optimization of pseudo‐continuous arterial spin labeling at 7T with parallel transmission B1 shimming