期刊
MAGNETIC RESONANCE IN MEDICINE
卷 60, 期 6, 页码 1422-1432出版社
JOHN WILEY & SONS INC
DOI: 10.1002/mrm.21739
关键词
parallel excitation; slice-selective excitation; RF inhomogeneity mitigation; multidimensional RF pulse; RF coil array
资金
- National Institute of Biomedical Imaging and Boengineering (NIBIB)
- National Institutes of Health (NIH) [R01EB006847, R01EB007942, R01EB000790]
- National Center for Research Resources (NCRR), NIH [P41RR14075]
- Siemens Medical Solutions
- R.J. Shillman Career Development Award
- MIND Institute
Slice-selective RF waveforms that mitigate severe B dagger inhomogeneity at 7 Tesla using parallel excitation were designed and validated in a water phantom and human studies on six subjects using a 16-element degenerate stripline array coil driven with a butler matrix to utilize the eight most favorable birdcage modes. The parallel RF waveform design applied magnitude least-squares (MLS) criteria with an optimized k-space excitation trajectory to significantly improve profile uniformity compared to conventional least-squares (LS) designs. Parallel excitation RF pulses designed to excite a uniform in-plane flip angle (FA) with slice selection in the z-direction were demonstrated and compared with conventional sinc-pulse excitation and RF shimming. In all cases, the parallel RF excitation significantly mitigated the effects of inhomogeneous B dagger on the excitation FA. The optimized parallel RF pulses for human B dagger mitigation were only 67% longer than a conventional sinc-based excitation, but significantly outperformed RF shimming. For example the standard deviations (SDs) of the in-plane FA (averaged over six human studies) were 16.7% for conventional sinc excitation, 13.3% for RF shimming, and 7.6% for parallel excitation. This work demonstrates that excitations with parallel RF systems can provide slice selection with spatially uniform FAs at high field strengths with only a small pulse-duration penalty. Magn Reson Med 60:1422-1432, 2008. (C) 2008 Wiley-Liss, Inc.
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