Ghosh Rajat K, Kuzma Nicholas N, Kadlecek Stephen J, Rizi Rahim R
Institutional Information: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Magn Reson Med. 2016 Apr;75(4):1822-30. doi: 10.1002/mrm.25679. Epub 2015 May 14.
Levitt and co-workers have described the M2S pulse sequence which transfers between longitudinal and singlet spin order. Building on this work, we describe the construction of a portable M2S pulse sequence generator to increase the relaxation time of polarized compounds. Additionally, we investigate the efficiency of spin order transfer under conditions where physical parameters of the system are not known precisely.
A portable M2S generator is built. Longitudinally polarized N2O is converted to the singlet state by both adiabatic transfer and by the M2S sequence. Density matrix simulations are used to model the effects of mismatched chemical shift, flip angle, and scalar couplings.
Density matrix simulations suggest that to convert 95% of the longitudinal m = 1 triplet state population to the singlet order we must match the Larmor precession frequency to the excitation radiofrequency field by 10%, the scalar couplings must be determined to better than 0.6%, and the flip angle must be calibrated to better than 2%.
The sequence is robust against many mismatched physical parameters of the species we are converting. Additionally, the instrument's portability allows for the conversion of hyperpolarized species near a polarizer. The lifetime is increased by ∼12-fold. This is highly advantageous in systems where the hyperpolarized media relax rapidly.
莱维特及其同事描述了在纵向和单重态自旋序之间转换的M2S脉冲序列。在此工作基础上，我们描述了一种便携式M2S脉冲序列发生器的构建，以延长极化化合物的弛豫时间。此外，我们研究了在系统物理参数不精确已知的条件下自旋序转移的效率。
构建了一台便携式M2S发生器。通过绝热转移和M2S序列将纵向极化的N2O转换为单重态。使用密度矩阵模拟来模拟化学位移失配、翻转角和标量耦合的影响。
密度矩阵模拟表明，要将95%的纵向m = 1三重态粒子数转换为单重态序，我们必须使拉莫尔进动频率与激发射频场匹配10%，标量耦合必须确定到优于0.6%，翻转角必须校准到优于2%。
该序列对我们正在转换的物质的许多失配物理参数具有鲁棒性。此外，仪器的便携性使得能够在极化器附近转换超极化物质。寿命增加了约12倍。这在超极化介质快速弛豫的系统中非常有利。
