A modification of the Single Point Imaging (SPI) is presented. The novel approach aims at increasing the sensitivity of the method and hence the resulting Signal-to-Noise ratio (SNR) for a given total time interval. With prior knowledge of the shape of the object under study, a selective sparse k-space sampling can then be used to follow dynamic phenomena of transient systems, in this case the absorption of moisture by a cereal-based wafer material. Further improvement in the image quality is achieved when the un-sampled k-space points are replaced by those of the initial dry or the final wet sample acquired at the beginning and the end of the acquisition respectively when there are no acquisition time limitations.

Two-dimensional (2D) T2-T2 molecular exchange NMR experiments with a period of magnetization storage between the two T2 relaxation encoding periods are presented. The two-dimensional time map was inverted using a fast Laplace algorithm to obtain the T2–T2 exchange map. T2–MZ(store)–T2 2D 1H NMR spectra recorded at high and low homogeneous magnetic fields of water and oil in sand, air bubbles in water and foams, exchange of liquid / foam and liquid / saturated vapours of chloroform are presented. Uni– and bi–directional exchange was observed for bubbles in water, superficial liquid shell, and foam.

Salt weathering is a major cause of deterioration of porous building materials. Of the salts responsible, especially sodium sulfate is seen as very damaging. However many questions arise concerning which sodium sulfate phase will crystallize out during salt weathering. In this study we focused on the crystallization during isothermal drying of a sample saturated with a sodium sulfate solution. As the material is drying moisture will leave and hence the salt concentration will rise until the maximum solubility is reached. From that point on crystals will be formed. Using NMR we have measured quasi simultaneously both the moisture and Na profiles during drying. These experiments have been performed at various temperatures and concentrations. In our NMR experiments we observe the formation of a metastable phase of sodium sulfate, the heptahydrate crystals.

Poly (Dimethyl siloxane) thin films were prepared by solvent evaporation method in porous alumina hosts. The thickness of these layers ranged from multilayer to sub-monolayer. Different NMR methods (FFC relaxometry, transverse relaxation, 1H Double quantum NMR) were applied to study the dynamics and order in these thin films. We found that dynamic restrictions and order increased with decreasing layer size. The increase of a short component of T2 from CPMG curves was attributed to the thawing of the adsorbed chains as seen in the decrease of the short component from Hahn echoes.

It is of interest in various scientific and industrial contexts to make a reliable estimation of the transport properties of porous media via more accessible probes such as NMR that yield information on static pore geometry and porosity. When the pore geometry is simple, there are empirical recipes that have long proven reliable in bridging the gap. For heterogeneous systems, such recipes fail to give a consistent prediction and invite case-by-case modifications. This is just one of many indications that the complex pore geometry erodes the predictive power of empirical laws that work well in simpler situations. Heterogeneity combined with sizeable diffusive coupling in extended pore space further undermines the validity of the MR interpretation based on simple pore geometry. On top of this, possible spatial variation of surface relaxivity may further complicate the interpretation. Resolution of these issues for real life samples requires elaborate simulations in tandem with experimental verifications on the shared pore geometry. We report on a recent progress which allows combined parallel Lattice Boltzmann and random walk simulations to study transport and diffusion properties in various types of pore geometry, from simple 2D micro-fluidic mazes, 3D glass-bead packs and sandstones to more complex carbonates.

This study presents the first demonstration of the MR signal decay due to diffusion in the internal field (DDIF) for in vivo knee trabecular bone imaging. DDIF contrast was compared with high resolution FLASH, T1, and T2* mapping in healthy volunteers. DDIF maps showed spatial variation, superimposed on a T1 background, reflecting trabecular structure. DDIF and T2* maps showed correlated contrast near dense trabeculae, but their spatial textures differed, suggesting distinct structural sensitivities.

In applications of NMR in inhomogeneous fields, sequences based on the Carr-Purcell-Meiboom-Gill (CPMG) sequence play a central role. The standard CPMG sequence consists of an initial 90° excitation pulse, followed by a long string of 180° refocusing pulses. This creates a series of echoes that decay with characteristic relaxation time T2eff. Here we present a modified sequence, the Split-180° sequence that specifically takes advantage of grossly inhomogeneous fields. In its simplest implementation, the 180° refocusing pulse of the CPMG sequence is split into two separate pulses. This sequence, which can be viewed as a modification of the CPMG sequence, simultaneously generates two types of signal that can be separately detected. One is a CPMG-like signal that decays with the expected relaxation time T2eff. In addition, a second type of signal builds up and approaches a steady-state. The amplitude of this dynamic equilibrium depends on the ratio of the longitudinal to the transverse relaxation times, T1/T2. We present experimental results and summarize the new theory that describes both signals in a unified manner.

The effects of molecular exchange processes on the two-dimensional (2D) NMR T2-T2 distributions obtained by Laplace inversion were studied by numerical simulations. The Monte–Carlo technique is used to generate free random walks of a large number of molecules within space regions characterized by different relaxation times. Molecular exchange processes are considered during CPMG encoding periods as well as during the storage period, τstore. Systematic simulations were performed as function of NMR parameters like the storage period, τstore and geometric or physical system properties.

We investigated the time-dependent self-diffusion coefficients of water, D(T eff), in polymer electrolyte membranes at 278 K. TheD(T eff) was measured from T eff=0.7 to 100 ms by field gradient NMR techniques. The results showed that the self-diffusion coefficients of water were dependent on T eff less than 2 ms due to restricted diffusion, and were constant beyond 3 ms. The tortuosity and surface-to-volume ratio related to water diffusion were also estimated from D(T eff). The obtained values revealed the existence of large-scale restricted geometry compared with well-known nanometer-sized domain in polymer electrolyte membranes.

Calcium sulphate hemihydrate (CaSO4·0.5H2O), commonly known as plaster of Paris, is used extensively in the construction, ceramics, and medical industries. There are two varieties of plaster referred to as α and β, produced by “wet” or “dry” methods respectively. Plaster hydrates to form crystalline gypsum (CaSO4·2H2O, dihydrate). We present a comparative in situ study of the microstructural changes that occur during the hydration of the two forms of plaster at a water-to-plaster ratio of w/p = 0.8 using NMR relaxometry and electron microscopy. In the α-plaster, pores evolve gradually to form a uniform, interconnected structure. In contrast, the β-plaster hydrates faster, leading to a less homogeneous product with micro-cracks resulting from rapid chemical shrinkage.