UNB MRI Centre, Department of Physics, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada.
J Magn Reson. 2021 May;326:106961. doi: 10.1016/j.jmr.2021.106961. Epub 2021 Mar 5.
The majority of low field Magnetic Resonance (MR) analyses rely on T lifetime measurements. Modification of the T measurement to include a T dimension has made the T-T measurement a very powerful analytical technique. The T-T measurement is uniquely well suited to characterization of different spin populations in porous materials, such as fluid bearing reservoir rocks, and in soft biopolymer materials, for example foods. However, the T-T measurement is challenging or impossible if the T relaxation lifetime, or a component lifetime, is short-lived and the signal unobservable in an echo measurement. This occurs in many important classes of materials. A short lifetime T will not however, in general, preclude observation of a free induction decay with signal decay governed by T*. As outlined in this paper a T-T* measurement is a useful analog to the T-T experiment. T-T* measurement enables one to differentiate species as a function of T* in one dimension and T in the other dimension. Monitoring changes of the T-T* coordinate, and associated signal intensity changes, has the potential to reveal structural changes in materials evolving in time. These methods may also be employed to discriminate and identify solid-like species present in static samples. The T-T* measurement is very general in application, but in this paper we focus on cement-based mortars to develop and illustrate the essential ideas. T-T* results show a multi-modal behaviour of the MR signal lifetimes, T and T*, in mortar samples under study, indicating at least two different water populations. The short T* lifetime was assigned to interlayer water (water between C-S-H layers) where the associated T is also short lived. The longer T* lifetime was assigned to water in the pore space, where T is also longer lived. In addition to mortar samples we also show application of the method to a crystalline organic species, o-phenylenediamine, which features Sinc Gaussian and exponential decays of transverse magnetization.
大多数低场磁共振（MR）分析依赖于 T 寿命测量。通过修改 T 测量以包括 T 维度，T-T 测量已成为一种非常强大的分析技术。T-T 测量非常适合于多孔材料中不同自旋群体的特征化，例如含流体的储层岩石，以及软生物聚合物材料，例如食品。然而，如果 T 弛豫寿命或组件寿命很短，并且在回波测量中信号不可见，则 T-T 测量具有挑战性或不可能。这种情况发生在许多重要的材料类别中。然而，一般来说，短寿命 T 不会排除通过由 T* 控制的信号衰减的自由感应衰减的观察。正如本文所述，T-T* 测量是 T-T 实验的有用模拟。T-T* 测量能够使我们能够在一个维度上根据 T* ，在另一个维度上根据 T 来区分物种。监测 T-T* 坐标的变化以及相关信号强度的变化，有可能揭示随时间演变的材料中的结构变化。这些方法也可用于区分和识别静态样品中存在的固态物质。T-T* 测量的应用非常广泛，但本文重点介绍基于水泥的砂浆，以开发和说明基本思想。T-T* 结果显示，研究中的砂浆样品的 MR 信号寿命 T 和 T* 具有多模态行为，表明至少存在两种不同的水群体。短 T* 寿命被分配给层间水（C-S-H 层之间的水），其中相关的 T 也寿命很短。较长的 T* 寿命被分配给孔隙空间中的水，其中 T 也寿命较长。除了砂浆样品，我们还展示了该方法在结晶有机物质邻苯二胺中的应用，该物质具有正弦高斯和横向磁化衰减的指数衰减。
