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

Kai Wang, Samantha J. Ma, Xingfeng Shao, Chenyang Zhao, Qinyang Shou, Lirong Yan, Danny J.J. Wang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: To optimize pseudo-continuous arterial spin labeling (pCASL) for 7 T, and to further improve the labeling efficiency with parallel RF transmission transmit B1 ((Formula presented.)) shimming. Methods: pCASL parameters were optimized based on (Formula presented.) field distributions at 7 T with simulation. To increase labeling efficiency, the (Formula presented.) amplitude at inflowing arteries was increased with parallel RF transmission (Formula presented.) 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 (Formula presented.) 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 (Formula presented.) 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, (Formula presented.)) achieved robust perfusion measurement in the presence of (Formula presented.) inhomogeneities. Both indv-shim and univ-shim significantly increased (Formula presented.) 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.

Original languageEnglish (US)
Pages (from-to)249-262
Number of pages14
JournalMagnetic resonance in medicine
Volume87
Issue number1
DOIs
StatePublished - Jan 2022
Externally publishedYes

Keywords

  • arterial spin labeling
  • B1+ shimming
  • parallel RF transmission
  • perfusion
  • ultrahigh field
  • universal pulse

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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