Slice-selective RF pulses for in vivo B1+ inhomogeneity mitigation at 7 tesla using parallel RF excitation with a 16-element coil.
Slice-selective RF pulses for in vivo B1+ inhomogeneity mitigation at 7 tesla using parallel RF excitation with a 16-element coil.
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DOI：
10.1002/mrm.21739
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发表时间：
2008-12
影响因子：
3.3
通讯作者：
Adalsteinsson, Elfar
中科院分区：
文献类型：
--
作者：
Setsompop, Kawin;Alagappan, Vijayanand;Gagoski, Borjan;Witzel, Thomas;Polimeni, Jonathan;Potthast, Andreas;Hebrank, Franz;Fontius, Ulrich;Schmitt, Franz;Wald, Lawrence L.;Adalsteinsson, Elfar
关键词：
使用平行激励在7 T下减轻严重B1+不均匀性的切片选择性RF波形在6名受试者的水模体和人体研究中设计并验证，使用Butler矩阵驱动的16元件简并带状线阵列线圈，以利用8种最有利的鸟笼模式。与传统的最小二乘设计相比，并行RF波形设计应用了幅度最小二乘标准和优化的k空间激励轨迹，以显著改善轮廓均匀性。平行激励RF脉冲设计用于激励均匀的平面内翻转角，在z方向上进行切片选择，并与传统的正弦脉冲激励和RF匀场进行了比较。在所有情况下，并行RF激励显著减轻了非均匀B1+对激励翻转角的影响。用于人体B1+缓解的优化并行RF脉冲仅比传统的基于sinc的激励长67%，但明显优于RF匀场。例如，平面内翻转角的标准偏差（六项人体研究的平均值）对于传统sinc激励为16.7%，对于RF匀场为13.3%，对于平行激励为7.6%。这项工作表明，激励与并行RF系统可以提供切片选择与空间均匀的翻转角在高场强只有一个小的脉冲持续时间惩罚。
Slice-selective RF waveforms that mitigate severe B1+ 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 8 most favorable birdcage modes. The parallel RF waveform design applied magnitude least squares criteria with an optimized k-space excitation trajectory to significantly improve profile uniformity compared to conventional least squares designs. Parallel excitation RF pulses designed to excite a uniform in-plane flip-angle with slice selection in the z-direction were demonstrated and compared to conventional sinc-pulse excitation and RF shimming. In all cases, the parallel RF excitation significantly mitigated the effects of inhomogeneous B1+ on the excitation flip-angle. The optimized parallel RF pulses for human B1+ mitigation were only 67% longer than a conventional sinc-based excitation, but significantly outperformed RF shimming. For example the standard deviations of the in-plane flip-angle (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 flip-angles at high field strengths with only a small pulse-duration penalty.
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