Zur Y, Wood M L, Neuringer L J
Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139.
Magn Reson Med. 1991 Oct;21(2):251-63. doi: 10.1002/mrm.1910210210.
A detailed analysis is presented of a method to eliminate transverse magnetization prior to each rf excitation in pulse sequences with TR less than T2. It is shown that artifact-free images with high T1 contrast can be obtained only if a phase shift that is incremented during each TR interval is applied to the transverse magnetization. Computer simulations are used to show that when this phase increment is 117 degrees, the steady-state transverse magnetization prior to each rf pulse is nulled over a wide range of T1, T2, and rf tip angles, resulting in optimal T1 contrast. Such nulling of steady-state transverse magnetization cannot be obtained by using large gradient pulses, or gradients of random or linearly incremented amplitude. Images of phantoms and human subjects confirm the theoretical predictions.
本文详细分析了一种在重复时间（TR）小于T2的脉冲序列中，于每次射频（rf）激发之前消除横向磁化的方法。结果表明，只有当在每个TR间隔内增加的相移应用于横向磁化时，才能获得具有高T1对比度且无伪影的图像。计算机模拟表明，当该相位增量为117度时，在较宽的T1、T2和rf翻转角范围内，每次rf脉冲之前的稳态横向磁化被消除，从而产生最佳的T1对比度。通过使用大梯度脉冲或幅度随机或线性增加的梯度，无法实现稳态横向磁化的这种消除。体模和人体受试者的图像证实了理论预测。
