RF peak power reduction in CAIPIRINHA excitation by interslice phase optimization
RF peak power reduction in CAIPIRINHA excitation by interslice phase optimization
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DOI：
10.1002/nbm.3360
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发表时间：
2015-11-01
影响因子：
2.9
通讯作者：
van den Berg, Cornelis A. T.
中科院分区：
文献类型：
--
作者：
Sbrizzi, Alessandro;Poser, Benedikt A.;van den Berg, Cornelis A. T.
这项工作的目的是表明，通过应用片间相位驰豫可以显著降低用于Caipirinha激发的RF脉冲的总峰值功率。最优相位依赖于扫描，并且可以用所提出的方法快速计算。多频段射频脉冲的设计被实现为具有二次约束的线性目标函数的最小化。片间相位被认为是用于优化的变量。在相位循环方案(Caipirinha)的情况下，考虑所有脉冲上的峰值功率。计算时间(约1s)与在线射频脉冲设计兼容。结果表明，最佳的片间相位取决于所采用的Caipirinha方案，并且当在优化中考虑Caipirinha相位循环时，射频峰值功率被降低。该方法速度极快，并能产生峰值功率较低的射频脉冲。附录中给出了MATLAB的实现；它允许在线确定扫描相关的相位参数。此外，该方法可以很容易地扩展到多层激励环境下的PTX垫片系统，并且这种可能性被包含在软件中。版权所有(C)2015 John Wiley&Sons，Ltd.
The purpose of this work was to show that the overall peak power of RF pulses for CAIPIRINHA excitation can be substantially reduced by applying interslice phase relaxation. The optimal phases are scan dependent and can be quickly calculated by the proposed method. The multi-band RF pulse design is implemented as the minimization of a linear objective function with quadratic constraints. The interslice phase is considered to be a variable for optimization. In the case of a phase cycling scheme (CAIPIRINHA), the peak power is considered over all pulses. The computation time (about 1s) is compatible with online RF pulse design. It is shown that the optimal interslice phases depend on the CAIPIRINHA scheme used and that RF peak power is reduced when the CAIPIRINHA phase cycling is taken into account in the optimization. The proposed method is extremely fast and results in RF pulses with low peak power for CAIPIRINHA excitation. The MATLAB implementation is given in the appendix; it allows for online determination of scan-dependent phase parameters. Furthermore, the method can be easily extended to pTx shimming systems in the context of multi-slice excitations, and this possibility is included in the software. Copyright (c) 2015 John Wiley & Sons, Ltd.