Davies Colin J, Griffith Jonathan D, Sederman Andrew J, Gladden Lynn F, Johns Michael L
Magnetic Resonance Research Centre, Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, UK.
J Magn Reson. 2007 Jul;187(1):170-5. doi: 10.1016/j.jmr.2007.04.006. Epub 2007 Apr 20.
Analysis of diffusion measurements as a function of observation time (Delta), to calculate surface-to-volume ratios (S/V) and tortuosities (kappa), is a useful tool in the characterisation of porous media using NMR. However, using conventional pulsed field gradient (PFG) measurements, this requires long total experiment times (typically hours). Here, we show how the rapid diffusion measurement pulse sequence, Difftrain, can be used to provide the required experimental data much more rapidly (typically within minutes) with a consequential reduction in total experiment time of typically over an order of magnitude. Several novel modifications to the Difftrain pulse sequence are also presented to tailor it to this particular application; these include a variable delay between echoes (to ensure optimal echo position with respect to Delta) and a variable tip angle for the refocusing pulse (to ensure optimal use of available signal). Difftrain is applied to measure both S/V and kappa for a model glass bead pack; excellent agreement is found with both a conventional PFG measurement and with a bulk gravimetric measurement of S/V.
作为观测时间（Δ）的函数对扩散测量进行分析，以计算表面积与体积比（S/V）和曲折度（κ），是使用核磁共振（NMR）表征多孔介质的一种有用工具。然而，使用传统的脉冲场梯度（PFG）测量，这需要很长的总实验时间（通常为数小时）。在此，我们展示了快速扩散测量脉冲序列Difftrain如何能够更快地（通常在几分钟内）提供所需的实验数据，从而使总实验时间相应减少，通常减少幅度超过一个数量级。还提出了对Difftrain脉冲序列的几种新颖修改，以使其适用于此特定应用；这些修改包括回波之间的可变延迟（以确保相对于Δ的最佳回波位置）和重聚焦脉冲的可变翻转角（以确保对可用信号的最佳利用）。Difftrain被应用于测量模型玻璃珠填充床的S/V和κ；发现其与传统PFG测量以及S/V的体积重量测量结果都有很好的一致性。
