PHASE ROBUST PULSE PAIRS FOR CHEMICAL SHIFT SELECTIVE SPIN ECHOES

导言：应用频率的一个重要副作用 选择性脉冲是在两个方向上引入相位梯度 频谱。翻转角度偏差约为5%-10% 更改脉冲通带上的相位分布。方法： 自旋回波的频率响应是从 90-180自旋-回波对中两个脉冲的Cayley-Klein参数。 为了设计脉冲，我们首先建立一个目标配置文件，它定义了 一对幅度调制脉冲的理想分布 B1不均质性。基于模拟退火法的最小二乘优化 然后用来找出使偏差最小的脉冲对 实际配置文件和目标配置文件之间的差异为+/-20% 在B1中。结果：脉冲以空间谱的形式实现 用于快速光谱成像实验的脉冲。 在感兴趣的体积上的相位变化的测量证实 相图的稳定性。结论：一种联合设计 90-180自旋回波对提供了不受UP影响的频率分布 到20%的射频同质性变化。

Introduction: An important side effect of applying a frequency selective pulse is the introduction of a phase gradient across the spectrum. Flip angle deviations on the order of 5-10% significantly change the phase profile across the passband of the pulse. Methods: The frequency response of a spin-echo is calculated from the Cayley-Klein parameters for the two pulses in a 90-180 spin-echo pair. To design the pulses we first establish a goal profile which defines the ideal profile for a pair of amplitude-modulated pulses subject to B1 inhomogeneity. Least squares optimization by simulated annealing is then used to find the pulse pair that minimizes the deviation between the actual profile and the goal profile, for +/-20% variation in B1. Results: The pulses were implemented as spatial-spectral pulses for use in a fast spectroscopic imaging experiment. Measurements of phase variations over the volume of interest confirmed the stability of the phase profile. Conclusions: A joint design of 90-180 spin-echo pairs offers frequency profiles that are immune to up to 20% variation in RF homogeneity.