Sørland G H, Seland J G, Krane J, Anthonsen H W
Department of Chemistry, Norwegian University of Science and Technology, Trondheim, N-7491, Norway.
J Magn Reson. 2000 Feb;142(2):323-5. doi: 10.1006/jmre.1999.1941.
The need for convection compensating methods in NMR has been manifested through an increasing number of publications related to the subject over the past few years (J. Magn. Reson. 125, 372 (1997); 132, 13 (1998); 131, 126 (1998); 118, 50 (1996); 133, 379 (1998)). When performing measurements at elevated temperature, small convection currents may give rise to erroneous values of the diffusion coefficient. In work with high resolution NMR spectroscopy, the application of magnetic field gradients also introduces an eddy-current magnetic field which may result in errors in phase and baseline in the FFT-spectra. The eddy current field has been greatly suppressed by the application of bipolar magnetic field gradients. However, when introducing bipolar magnetic field gradients, the pulse sequence is lengthened significantly. This has recently been pointed out as a major drawback because of the loss of coherence and of NMR-signal due to transverse relaxation processes. Here we present modified convection compensating pulsed field gradient double spin echo and double stimulated echo sequences which suppress the eddy-current magnetic field without increasing the duration of the pulse sequences.
在过去几年中，越来越多与该主题相关的出版物表明了核磁共振（NMR）中对流补偿方法的必要性（《磁共振杂志》125卷，372页（1997年）；132卷，13页（1998年）；131卷，126页（1998年）；118卷，50页（1996年）；133卷，379页（1998年））。在高温下进行测量时，小的对流电流可能会导致扩散系数的错误值。在高分辨率核磁共振光谱学研究中，磁场梯度的应用还会引入一个涡流磁场，这可能会导致快速傅里叶变换（FFT）光谱中的相位和基线出现误差。通过应用双极磁场梯度，涡流磁场已得到极大抑制。然而，在引入双极磁场梯度时，脉冲序列会显著延长。最近，这被指出是一个主要缺点，因为横向弛豫过程会导致相干性和NMR信号的损失。在此，我们提出了改进的对流补偿脉冲场梯度双自旋回波和双受激回波序列，它们在不增加脉冲序列持续时间的情况下抑制了涡流磁场。
