Nuclear Magnetic Resonance Imaging Measurements Research Articles

Pore Distribution Characteristics of Thawed Residual Soils in Artificial Frozen-Wall Using NMRI and MIP Measurements

Artificial ground freezing method is widely applied in the construction of metro tunnel and significantly impact the microstructure of soils in artificial frozen-walls. To delve into the pore distribution characteristics of thawed residual soils, Nuclear Magnetic Resonance Imaging (NMRI) measurements were performed to investigate the relaxation time (T2) spectrums and T2-weighted images of saturated samples after freezing at different temperatures. The pore volume distributions were determined from T2 spectrums based on the surface relaxation coefficient ( ρ 2 ) and the pore structures were visualized by T2-weighted images. Subsequently, the pore size distribution curves from NMRI were compared and validated by mercury intrusion porosimetry (MIP) tests. According to the results, the peak areas of T2 spectrums were linearly related to freezing temperatures in a positive manner. Pore volume distribution curves of thawed soils have two peaks, which are the major peaks with diameters of 0.5–20 μm and the secondary peaks with diameters of 20–500 μm. As the freezing temperature drops, the volumes of pores with different diameters all increased. The damage degree of microstructure in thawed soils increases as the temperature drops, according to the visualized pore structure. Besides, NMRI measurements of saturated soils are more accurate to reflect the full diameter range of pores, compared to MIP method.

Water ingress in Y-type zeolite: Anomalous moisture-dependent transport diffusivity

Nuclear magnetic resonance imaging measurements of liquid water ingress in a large number of nonactivated Y-type (Na) zeolite samples prepared under different conditions are reported on. Using an experimental arrangement that permits the application of Boltzmann's transformation of the 1D (one-dimensional) diffusion equation, the spatiotemporal scaling variables required for a collapse of the measured profiles into universal curves revealed subdiffusive behavior in all cases. It is shown that the one-dimensional fractal time diffusion equation constitutes a powerful tool to analyze the data and provides a connection between the moisture dependence of the effective transport diffusivities and the shapes of the universal curves. Thus, even for anomalous diffusion, the relationship between the universal curves and structural characteristics of the system; such as porosity, tortuosity of the pore space and, in some cases, the interplay between mesopores and nanopores can be addressed.

Magnetic resonance imaging of moisture distribution in Pinus sylvestris L. exposed to daily indoor relative humidity fluctuations

In contact with indoor air, wood materials have a high potential passively to reduce the indoor humidity fluctuations resulting from internal moisture loads and outdoor humidity fluctuations. This ability, characterized by the moisture buffering capacity of building materials, has attracted increasing attention within building physics, but a suitable method to appraise and quantify this phenomenon is still sought. In this study, a non-invasive spectroscopic method of accessing information about the interaction between indoor air and Scots pine was investigated. A comprehensive account is given of spatially resolved moisture absorption (desorption) into (from) Scots pine by proton magnetic resonance imaging ([1H]MRI) based on an effective single-point imaging (SPI) sequence. SPI images of bound-water distribution in Scots pine with a spatial resolution on a sub-millimetre scale were acquired when one of the orthotropic directions of the wood material was exposed to typical indoor day-to-day moisture fluctuations. The nuclear magnetic resonance imaging measurements presented in this study clearly show the potential of the method to provide accurate spatial information about the wood–water interaction below the fibre saturation point and hence to characterize the moisture buffering capacity of wood materials.

Nuclear Magnetic Resonance Imaging for Studies of Flow and Transport in Porous Media

Nuclear magnetic resonance imaging (NMRI) methods for visualization of fluid flow and transport in porous media are reviewed in this paper. They are illustrated with experiments showing applications of velocity imaging, NMRI measurements of multiphase flow, and NMRI measurements of density flow. The latter two are compared with numerical simulations. The examples show the capacity of NMRI to give structural information both of the medium and the fluid distributions as well as their temporal development. The resulting data can be used in a black box-white box comparison and as benchmarks for numerical models.

Nuclear Magnetic Resonance Imaging for Studies of Flow and Transport in Porous Media

Nuclear magnetic resonance imaging (NMRI) methods for visualization of fluid flow and transport in porous media are reviewed in this paper. They are illustrated with experiments showing applications of velocity imaging, NMRI measurements of multiphase flow, and NMRI measurements of density flow. The latter two are compared with numerical simulations. The examples show the capacity of NMRI to give structural information both of the medium and the fluid distributions as well as their temporal development. The resulting data can be used in a black box–white box comparison and as benchmarks for numerical models.

Nuclear magnetic resonance imaging measurements of water diffusion in the perfused hippocampal slice during N-methyl- d-aspartate-induced excitotoxicity

Significant changes in the apparent diffusion coefficient of water are observed in nuclear magnetic resonance images of patients with acute ischemic stroke. However, the underlying mechanisms of these apparent diffusion coefficient changes are still unresolved. To analyse possible mechanisms, this study applies nuclear magnetic resonance imaging on a 14.1 Tesla narrow-bore magnet to quantitatively study water diffusion in individually perfused brain slices following exposure to N-methyl- d-aspartate excitotoxicity. The results indicate that brain slices have at least two distinct diffusing water compartments with apparent diffusion coefficients of 0.96±0.10×10 −3 mm 2/s and 0.06±0.01×10 −3 mm 2/s. When excitotoxicity was induced with N-methyl- d-aspartate, there was a significant decrease in the fraction of the fast diffusing water component in the slices ( P<0.001). However, neither apparent diffusion coefficient changed significantly. Prior treatment with dizocilpine maleate (MK-801) depressed the effects of N-methyl- d-aspartate ( P<0.01, ANOVA). The results demonstrate brain slice compartmental changes resulting from direct receptor stimulation and provide evidence for tissue water redistribution as an important mechanism for changes in apparent diffusion coefficient seen in clinical magnetic resonance imaging. The brain slice preparation affords a well-controlled method to study the mechanisms of tissue nuclear magnetic resonance contrast, bridging the gap between basic nuclear magnetic resonance studies and clinical magnetic resonance imaging. The brain slice model also offers a new way to test the utility of potential anti-stroke drugs using high field nuclear magnetic resonance imaging.