Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, USA.
Magn Reson Med. 2018 Feb;79(2):701-710. doi: 10.1002/mrm.26720. Epub 2017 May 12.
To introduce a method of designing single and parallel transmit (pTx) 3D adiabatic π pulses for inverting and refocusing spins that are insensitive to transmit B ( B1+) inhomogeneity.
A 3D adiabatic pulse is created by replacing each piece-wise constant element (or sub-pulse) of an adiabatic full passage (AFP) by a 2D selective pulse. In this study, the parent AFP is an HS1 and each sub-pulse is a 2D pulse derived from a jinc function designed using a spiral k-trajectory. Spatial selectivity in the third direction is achieved by blipping the slab-selective gradient between sub-pulses, yielding a rectangular slab profile identical to that of the parent AFP. The slew-rate limited sub-pulse can be undersampled utilizing pTx, thus shortening the overall pulse width. Simulations and experiments demonstrate the quality of spatial selectivity and adiabaticity achievable.
The 3D adiabatic pulse inverts and refocus spins in a sharply demarcated cylindrical volume. When stepping RF amplitude, an adiabatic threshold is observed above which the flip angle remains π. Experimental results demonstrate that pTx is an effective means to significantly improve pulse performance.
A method of designing 3D adiabatic pulses insensitive to B inhomogeneity has been developed. pTx can shorten these pulses while retaining their adiabatic character. Magn Reson Med 79:701-710, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
介绍一种设计单路和并行发射（pTx）3D 绝热 π 脉冲的方法，用于反转和聚焦对发射 B1+不均匀性不敏感的自旋。
通过用 2D 选择性脉冲替换绝热全通（AFP）中每个分段常数元件（或子脉冲），来创建 3D 绝热脉冲。在本研究中，母 AFP 为 HS1，每个子脉冲是从基于螺旋 k 轨迹设计的 jinc 函数导出的 2D 脉冲。通过在子脉冲之间闪烁片选梯度，可以在第三个方向上实现空间选择性，从而产生与母 AFP 相同的矩形片层轮廓。采用 pTx 可以对限幅斜率子脉冲进行欠采样，从而缩短整体脉冲宽度。仿真和实验证明了可实现的空间选择性和绝热性的质量。
3D 绝热脉冲可在清晰界定的圆柱形体积内反转和聚焦自旋。当逐步提高 RF 幅度时，会观察到一个绝热阈值，在此阈值之上翻转角保持为π。实验结果表明，pTx 是显著改善脉冲性能的有效手段。
已经开发出一种设计对 B 不均匀性不敏感的 3D 绝热脉冲的方法。pTx 可以在保持其绝热特性的同时缩短这些脉冲。磁共振医学 79:701-710, 2018。© 2017 国际磁共振学会。
