Spontaneous emission of NMR signals in hyperpolarized proton spin systems
Spontaneous emission of NMR signals in hyperpolarized proton spin systems
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DOI：
10.1016/j.jmr.2010.11.002
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发表时间：
2011-02-01
影响因子：
2.2
通讯作者：
Hilty, Christian
中科院分区：
文献类型：
--
作者：
Chen, Hsueh-Ying;Lee, Youngbok;Hilty, Christian
核自旋的超极化作为改善NMR和MRI的信噪比的工具越来越受到关注。虽然在原则上，超极化的样品服从于与常规NMR中使用的相同或相似的实验，但大的自旋极化可能会产生意想不到的效果。在这里，从质子自旋系统中观察到信号的自发发射，该质子自旋系统通过动态核极化（DNP）被超极化到负自旋温度。这些发射的一个意想不到的特征是，在没有任何射频激励的情况下，多个拍频出现，这不能用具有辐射阻尼的布洛赫方程来解释。然而，我们表明，这些方程的一个简单的修改，它考虑到额外的供应超极化磁化从水库以外的主动检测区域，可以现象学地描述所观察到的信号。观察到的效果表明，即使是众所周知的自旋演化机制可以产生意想不到的效果时，与超极化的样品，这可能需要通过开发新的实验技术来解决。(C)2010年爱思唯尔公司All rights reserved.
Hyperpolarization of nuclear spins is gaining increasing interest as a tool for improving the signal-to-noise ratio of NMR and MRI. While in principle, hyperpolarized samples are amenable to the same or similar experiments as are used in conventional NMR, the large spin polarization may give rise to unexpected effects. Here, spontaneous emission of signal was observed from proton spin systems, which were hyperpolarized to negative spin temperature by dynamic nuclear polarization (DNP). An unexpected feature of these emissions is that, without any radio-frequency excitation, multiple beats arise that cannot be explained by the Bloch equations with radiation damping. However, we show that a simple modification to these equations, which takes into account an additional supply of hyperpolarized magnetization from a reservoir outside of the active detection region, can phenomenologically describe the observed signal. The observed effect demonstrates that even well-known mechanisms of spin evolution can give rise to unexpected effects when working with hyperpolarized samples, which may need to be addressed through the development of new experimental techniques. (C) 2010 Elsevier Inc. All rights reserved.