Department of Chemistry, Duke University, Durham, NC, 27708, USA.
Department of Chemistry, Karmanos Cancer Institute (KCI), Wayne State University, Detroit, MI, 48202, USA.
Nat Commun. 2019 Jan 23;10(1):395. doi: 10.1038/s41467-019-08298-8.
Signal amplification by reversible exchange (SABRE) is an efficient method to hyperpolarize spin-1/2 nuclei and affords signals that are orders of magnitude larger than those obtained by thermal spin polarization. Direct polarization transfer to heteronuclei such as C or N has been optimized at static microTesla fields or using coherence transfer at high field, and relies on steady state exchange with the polarization transfer catalyst dictated by chemical kinetics. Here we demonstrate that pulsing the excitation field induces complex coherent polarization transfer dynamics, but in fact pulsing with a roughly 1% duty cycle on resonance produces more magnetization than constantly being on resonance. We develop a Monte Carlo simulation approach to unravel the coherent polarization dynamics, show that existing SABRE approaches are quite inefficient in use of para-hydrogen order, and present improved sequences for efficient hyperpolarization.
信号放大可逆交换（SABRE）是一种高效的极化自旋-1/2 核的方法，其产生的信号比热自旋极化方法获得的信号大几个数量级。直接极化转移到异核，如 C 或 N，已经在静态微特斯拉场中得到优化，或者在高场中使用相干转移得到优化，并且依赖于化学动力学决定的极化转移催化剂的稳态交换。在这里，我们证明了脉冲激发场会诱导复杂的相干极化转移动力学，但实际上在共振时以大约 1%的占空比进行脉冲比一直保持在共振时产生更多的磁化。我们开发了一种蒙特卡罗模拟方法来揭示相干极化动力学，表明现有的 SABRE 方法在利用 Para-Hydrogen Order 时效率相当低，并提出了用于高效极化的改进序列。
