PHASE ROBUST PULSE PAIRS FOR CHEMICAL SHIFT SELECTIVE SPIN ECHOES

简介：应用频率的一个重要副作用 选择性脉冲是在整个相位梯度的引入， 江西篇章 翻转角度偏差约为5-10%， 改变脉冲通带上的相位分布。 研究方法： 自旋回波的频率响应是根据 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轮廓， 一对调幅脉冲的理想轮廓， B1不均匀性。 模拟退火最小二乘优化 然后用于找到使偏差最小化的脉冲对 实际曲线和目标曲线之间，+/-20%变化 在B1。 结果：脉冲实现为空间-光谱 用于快速光谱成像实验的脉冲。 在感兴趣的体积上测量相位变化， 相位分布的稳定性。 结论：关节设计 90-180自旋回波对提供的频率配置文件，是免疫向上 射频均匀性的变化可达20%。

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.