Storage of nuclear magnetization as long-lived singlet order in low magnetic field
Storage of nuclear magnetization as long-lived singlet order in low magnetic field
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DOI：
10.1073/pnas.1010570107
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发表时间：
2010-10-05
影响因子：
11.1
通讯作者：
Levitt, Malcolm H.
中科院分区：
文献类型：
--
作者：
Pileio, Giuseppe;Carravetta, Marina;Levitt, Malcolm H.
超极化核态提供了增强了许多数量级的NMR信号，具有分析NMR、体内NMR和NMR成像的许多潜在应用。然而，超极化磁化的寿命通常受到弛豫时间常数T（1）的限制，除了在例外情况下，弛豫时间常数T（1）在毫秒到分钟的范围内。在许多情况下，超极化状态的寿命可以通过将磁化强度转换为核单重态顺序来增强，其中它被保护免受许多常见的弛豫机制的影响。然而，目前所有将磁化强度转换为单线态的方法都需要使用高场、高均匀性的NMR磁体，这与大多数超极化程序不兼容。我们展示了一种新的方法，用于将磁化转换为单重态顺序，并再次返回。新技术适用于弱磁场和非均匀磁场中的磁不等效自旋对系统，并且与已知的超极化技术兼容。该方法涉及在低场核拉莫尔频率下的音频脉冲照射，采用180度脉冲的耦合同步序列来诱导单重态-三重态跃迁。回波链被用作称为M2 S的脉冲序列的构建块，该脉冲序列将纵向磁化转换为长寿命的单重态顺序。称为S2 M的脉冲序列的时间反转将单重态顺序转换回纵向磁化。该方法在（15）N-标记的一氧化二氮溶液上进行了证明。磁化强度在低磁场中储存超过30 min，即使在相同条件下T（1）小于3 min。
Hyperpolarized nuclear states provide NMR signals enhanced by many orders of magnitude, with numerous potential applications to analytical NMR, in vivo NMR, and NMR imaging. However, the lifetime of hyperpolarized magnetization is normally limited by the relaxation time constant T(1), which lies in the range of milliseconds to minutes, apart from in exceptional cases. In many cases, the lifetime of the hyperpolarized state may be enhanced by converting the magnetization into nuclear singlet order, where it is protected against many common relaxation mechanisms. However, all current methods for converting magnetization into singlet order require the use of a high-field, high-homogeneity NMR magnet, which is incompatible with most hyperpolarization procedures. We demonstrate a new method for converting magnetization into singlet order and back again. The new technique is suitable for magnetically inequivalent spin-pair systems in weak and inhomogeneous magnetic fields, and is compatible with known hyperpolarization technology. The method involves audio-frequency pulsed irradiation at the low-field nuclear Larmor frequency, employing coupling-synchronized trains of 180 degrees pulses to induce singlet-triplet transitions. The echo trains are used as building blocks for a pulse sequence called M2S that transforms longitudinal magnetization into long-lived singlet order. The time-reverse of the pulse sequence, called S2M, converts singlet order back into longitudinal magnetization. The method is demonstrated on a solution of (15)N-labeled nitrous oxide. The magnetization is stored in low magnetic field for over 30 min, even though the T(1) is less than 3 min under the same conditions.