Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
Magn Reson Med. 2017 Dec;78(6):2185-2193. doi: 10.1002/mrm.26610. Epub 2017 Jan 17.
Multiband pulses are characterized by highly temporally modulated waveforms. Rapid phase or frequency modulation can be extremely demanding on the performance of radiofrequency (RF) pulse generation, which can lead to errors that can be avoided if pulses are restricted to amplitude modulation (AM) only. In this work, three existing multiband pulse design techniques are modified to produce AM waveforms.
Multiband refocusing pulses were designed using phase-optimization, time-shifting, and root-flipping. Each technique was constrained to produce AM pulses by exploiting conjugate symmetry in their respective frequency domain representations. Pulses were designed using the AM and unconstrained techniques for a range of multiband factors (ie, number of simultaneously excited slices), time-bandwidth products, and slice separations. Performance was compared by examining the resulting effective pulse durations. Phantom and in vivo experiments were conducted for validation.
Acquired data confirmed that AM pulses can produce precise results when unconstrained designs may produce artifacts. The average duration of AM pulses is longer than the unconstrained versions. Averaged across a range of parameters, the duration cost for AM pulses was 26, 38, and 20% for phase-optimizing, time-shifting and root-flipping, respectively.
Amplitude modulation multiband pulses can be produced for a relatively small increase in pulse duration. Magn Reson Med 78:2185-2193, 2017. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
多带脉冲的特点是具有高度时间调制的波形。快速的相位或频率调制对射频 (RF) 脉冲产生的性能要求极高，如果仅限制脉冲进行幅度调制 (AM)，则可以避免这些性能要求。在这项工作中，对三种现有的多带脉冲设计技术进行了修改，以产生 AM 波形。
使用相位优化、时移和根翻转设计多带重聚脉冲。每种技术都通过利用其各自的频域表示中的共轭对称性来限制产生 AM 脉冲。使用 AM 和非约束技术设计了一系列多带因子（即同时激励的切片数量）、时带宽积和切片分离的多带脉冲。通过检查所得有效脉冲持续时间来比较性能。进行了幻影和体内实验以进行验证。
获得的数据证实，当非约束设计可能产生伪影时，AM 脉冲可以产生精确的结果。AM 脉冲的平均持续时间长于非约束版本。在一系列参数中平均，相位优化、时移和根翻转的 AM 脉冲的持续时间成本分别为 26%、38%和 20%。
可以在相对较小的脉冲持续时间增加的情况下产生 AM 多带脉冲。磁共振医学 78：2185-2193，2017。© 2017 作者磁共振医学由 Wiley 期刊出版公司代表国际磁共振医学协会出版。这是根据知识共享署名许可条款允许在任何媒介中使用、分发和复制原始作品的条款，只要原始作品正确引用。
