Heid O
Institute of Diagnostic Radiology, University of Bern, Switzerland.
Magn Reson Med. 1997 Oct;38(4):585-90. doi: 10.1002/mrm.1910380413.
A theory of optimum burst excitation is developed in the framework of the Shinnar-LeRoux spinor formalism. An N pulse RF train of constant or linear phase cannot improve on an average echo strength of M0/N, and a phase modulation of the pulse train is necessary to improve the signal yield to the theoretical maximum value M0 square root of N. Several methods are presented yielding pulse trains of nearly optimum average amplitude for arbitrary N. It is shown that RF phase spoiling can be analyzed with the same framework. The presented pulse trains may also be useful when ultrawide spectrum hard pulses are required, but only limited RF power is available, e.g., for NMR experiments in extremely inhomogeneous B0 fields.
在Shinnar-LeRoux旋量形式体系的框架下，发展了一种最优脉冲串激励理论。恒定或线性相位的N脉冲射频序列，其平均回波强度无法超过M0/N，必须对脉冲序列进行相位调制，才能将信号产率提高到理论最大值M0√N。文中给出了几种方法，可针对任意N生成平均幅度接近最优的脉冲序列。结果表明，射频相位破坏也可在同一框架下进行分析。当需要超宽谱硬脉冲，但可用射频功率有限时，如在极不均匀B0场中的核磁共振实验，所提出的脉冲序列可能也很有用。
