Pfaff Annalise R, McKee Cailyn E, Woelk Klaus
Department of Chemistry, Missouri University of Science & Technology, 400 West 11th, Rolla, MO 65409-0010, USA.
J Magn Reson. 2017 Nov;284:99-103. doi: 10.1016/j.jmr.2017.09.014. Epub 2017 Oct 3.
Adiabatic half and full passages are invaluable for achieving uniform, B-insensitive excitation or inversion of macroscopic magnetization across a well-defined range of NMR frequencies. To accomplish narrow frequency ranges with adiabatic pulses (<100Hz), long pulse durations at low RF power levels are necessary, and relaxation during these pulses may no longer be negligible. A numerical, discrete recursive combination of the Bloch equations for longitudinal and transverse relaxation with the optimized equation for adiabatic angular motion of magnetization is used to calculate the trajectory of magnetization including its relaxation during adiabatic hyperbolic secant pulses. The agreement of computer-calculated data with experimental results demonstrates that, in non-viscous, small-molecule fluids, it is possible to model magnetization and relaxation by considering standard T and T relaxation in the traditional rotating frame. The proposed model is aimed at performance optimizations of applications in which these pulses are employed. It differs from previous reports which focused on short high-power adiabatic pulses and relaxation that is governed by dipole-dipole interactions, cross polarization, or chemical exchange.
绝热半程和全程脉冲对于在明确定义的核磁共振频率范围内实现宏观磁化的均匀、B 不敏感激发或反转非常重要。为了用绝热脉冲实现窄频率范围（<100Hz），在低射频功率水平下需要长脉冲持续时间，并且这些脉冲期间的弛豫可能不再可忽略。使用纵向和横向弛豫的布洛赫方程与磁化绝热角运动的优化方程的数值离散递归组合来计算磁化轨迹，包括其在绝热双曲正割脉冲期间的弛豫。计算机计算数据与实验结果的一致性表明，在非粘性小分子流体中，通过在传统旋转坐标系中考虑标准 T1 和 T2 弛豫来模拟磁化和弛豫是可能的。所提出的模型旨在对使用这些脉冲的应用进行性能优化。它与之前专注于短高功率绝热脉冲以及由偶极 - 偶极相互作用、交叉极化或化学交换控制的弛豫的报告不同。
