Reducing the duration of broadband excitation pulses using optimal control with limited RF amplitude
Reducing the duration of broadband excitation pulses using optimal control with limited RF amplitude
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DOI：
10.1016/j.jmr.2003.12.001
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发表时间：
2004-03-01
影响因子：
2.2
通讯作者：
Glaser, SJ
中科院分区：
文献类型：
--
作者：
Skinner, TE;Reiss, TO;Glaser, SJ
将最优控制理论与新的射频限制步骤相结合，在给定的最大射频幅度下，与先前的优化脉冲(BEBOP)宽带激励相比，产生的脉冲具有显著缩短的持续时间和更好的性能。产生的脉冲可以容忍与标准高分辨率核磁共振探头相关的射频同质性的变化。设计标准是I-z-->；i-x在+/-20 kHz的共振偏移量和+/-5%的RF变异性上的变换，脉冲长度为500微秒，峰值RF幅度等于17.5 kHz。在超过设计目标的谐振偏移量和射频变化量范围内，仿真将i-z变换为大于0.995 i-x，最终磁化的相位偏差小于2度。该脉冲的实验性能与仿真结果吻合良好。还研究了对于更短的脉冲或具有降低的数字化的脉冲的性能权衡。(C)2003 Elsevier Inc.保留所有权利。
Combining optimal control theory with a new RF limiting step produces pulses with significantly reduced duration and improved performance for a given maximum RF amplitude compared to previous broadband excitation by optimized pulses (BEBOP). The resulting pulses tolerate variations in RF homogeneity relevant for standard high-resolution NMR probes. Design criteria were transformation of I-z --> I-x over resonance offsets of +/-20 kHz and RF variability of +/-5%, with a pulse length of 500 mus and peak RF amplitude equal to 17.5 kHz. Simulations transform I-z to greater than 0.995 I-x, with phase deviations of the final magnetization less than 2degrees, over ranges of resonance offset and RF variability that exceed the design targets. Experimental performance of the pulse is in excellent agreement with the simulations. Performance tradeoffs for yet shorter pulses or pulses with decreased digitization are also investigated. (C) 2003 Elsevier Inc. All rights reserved.