Root-flipped multiband refocusing pulses.
Root-flipped multiband refocusing pulses.
复制标题
DOI：
10.1002/mrm.25629
复制
发表时间：
2016-01
影响因子：
3.3
通讯作者：
Grissom WA
中科院分区：
文献类型：
--
作者：
Sharma A;Lustig M;Grissom WA
设计低峰值功率多频带再聚焦射频（RF）脉冲，应用于同步多层自旋回波MRI。采用凸优化方法设计了多带Shinnar-Le Roux β多项式。蒙特卡罗算法用于确定β多项式根翻转的模式，其最小化所得重聚焦脉冲的峰值功率。相位匹配的多波段激发脉冲也被设计成获得线性相位自旋回波。仿真比较了根翻转脉冲与时移和相位优化脉冲的性能。在7 T下的体模和体内实验验证了根翻转脉冲的功能，并将其与时移自旋回波信号曲线进行了比较。在切片数、时间带宽积和切片间隔上取平均值，根翻转脉冲的持续时间比具有相同峰值RF幅度的时移脉冲短46%。与时移和相位优化脉冲不同，根翻转脉冲的激励误差不会随着频带间隔的减小而增加。实验表明，根翻转脉冲在目标位置处激发所需切片，并且对于等效切片特性，较短的根翻转脉冲允许较短的回波时间，从而导致比时移脉冲更高的信号。所提出的根翻转多频带RF脉冲设计方法产生用于同时多层自旋回波MRI的低峰值功率脉冲。
To design low peak power multiband refocusing radiofrequency (RF) pulses, with application to simultaneous multislice spin echo MRI. Multiband Shinnar-Le Roux β polynomials were designed using convex optimization. A Monte Carlo algorithm was used to determine patterns of β polynomial root flips that minimized the peak power of the resulting refocusing pulses. Phase-matched multiband excitation pulses were also designed to obtain linear-phase spin echoes. Simulations compared the performance of the root-flipped pulses with time-shifted and phase-optimized pulses. Phantom and in vivo experiments at 7 T validated the function of the root-flipped pulses and compared them to time-shifted spin echo signal profiles. Averaged across number of slices, time-bandwidth product, and slice separation, the root-flipped pulses have 46% shorter durations than time-shifted pulses with the same peak RF amplitude. Unlike time-shifted and phase-optimized pulses, the root-flipped pulses excitation errors do not increase with decreasing band separation. Experiments showed that the root-flipped pulses excited the desired slices at the target locations, and that for equivalent slice characteristics, the shorter root-flipped pulses allowed shorter echo times, resulting in higher signal than time-shifted pulses. The proposed root-flipped multiband RF pulse design method produces low peak power pulses for simultaneous multislice spin echo MRI.