Nuclear Magnetic Resonance Imaging Techniques Research Articles

NMR imaging experiments for the verification of stochastic transport theory

Nuclear magnetic resonance (NMR) imaging techniques were investigated as a means to obtain velocity field measurements for the verification of a stochastic transport theory. A modified stimulated-echo pulse sequence was used to make velocity images in an aperiodic heterogeneous porous medium. Construction of the velocity covariance from measurements of the fluctuating velocity has demonstrated that nuclear magnetic resonance imaging is a valuable tool for obtaining experimental data for the examination of existing stochastic transport theory.

Evaluation of chemically-induced pore surface modifications on rock cores

Chemical modification of pore surface properties due to active components of crude oils could significantly affect production processes. Specific chemical treatments can prevent surface alteration, protecting pores from deposition of heavy oils components. Both relaxation times analysis and nuclear magnetic resonance (NMR) imaging technique are a valuable method for nondestructive monitoring of solid/liquid interface alteration especially if applied to heterogeneous rock cores, which are impossible to study using conventional methods (e.g., Amott tests and dynamic angle contact). In our work, we examined carbonate core plugs subjected to aging treatments in crude oil. Relaxation times measurement, revealing modifications of fluid/surface interactions and imaging, was applied in characterise heterogeneous systems and reveal fluid distribution changes. Nuclear magnetic resonance results were compared with a special microscopy technique (Cryo-SEM) that allows observation of fluids at the pore level, providing a better understanding of the processes involved.

Experimental observation of fluid flow channels in a single fracture

A method for obtaining precise replicas of real fracture surfaces using transparent epoxy resins was developed, allowing detailed study of fluid flow paths within a fracture plane. A natural rock fracture was collected from the field and prepared for study. Silicon rubber molds of the fracture surfaces were used to make a transparent epoxy replica of the original fracture. Clear and dyed water were injected into the fracture pore space allowing examination of the flow field. Digitized optical images were used to observe wetting, saturated flow, and drying of the specimen. Nuclear magnetic resonance imaging was used for quantitative measurements of flow velocity. Both video imaging and nuclear magnetic resonance imaging techniques show distinct and strong channeling of the flow at the submillimeter to several‐centimeter scale. Each phenomenon, including wetting, drying, dye transport, and velocity channeling, has its own distinct geometric structure and scale. We find that fluid velocities measured simultaneously at various locations in the fracture plane during steady state flow range over several orders of magnitude, with the maximum velocity a factor of 5 higher than the mean velocity. This suggests that flow channeling in fractured rock can cause the breakthrough velocity of contaminants to far exceed the mean flow.

NMR Imaging of Immiscible Displacements in Porous Media

Summary We introduce a rapid, quantitative nuclear magnetic resonance imaging (NMRI) technique to resolve and measure multiple fluid phases in porous media. Liquids are resolved on the basis of their NMR spin-spin (T2) relaxation times, and their intensities are corrected by attenuation analysis. The phase-resolved and corrected NMRI intensities are normalized to yield fluid saturations. We present the procedure and limitations of this technique. We present in-situ saturation measurements for three immiscible (oil and water) displacements in the same Berea sandstone core. We compared NMRI and effluent recovery methods. T2 of the displacement fluids were sensitive to displacement conditions.

Capillary penetration in fibrous matrices studied by dynamic spiral magnetic resonance imaging

The dynamic spiral nuclear magnetic resonance (NMR) imaging technique was used to investigate the water imbibition into cellulose fiber matrices. The advancing water boundary, water concentration distribution, and swelling degree within the fiber matrix samples were monitored as a function of time over the entire absorption process. A combined image that shows the time evolution of the absorbed water concentration distribution within the fiber matrix was synthesized from the dynamically acquired NMR image data set. The NMR imaging data clearly demonstrated that water imbibition into a fiber matrix consists of two different processes: water penetration into capillaries between fibers and water diffusion into the cellulose fibers. The advancing liquid front is primarily determined by the water capillary flow and can be quantitatively described by Washburn equation. The slower water diffusion process in fibers is mainly responsible for the fiber swelling. The time evolution of the absorbed water concentration distribution can be qualitatively interpreted in terms of steady capillary flow and concentration-gradient-driven diffusion into fibers with a constant permeability. The effects of pore morphology, tortuosity, and surface heterogeneity to the water absorption process are also discussed.

Nuclear Magnetic Resonance Imaging Detects Internal Defects in Potatoes

Potatoes with hollow heart or brown center are considered to be of poor quality for both fresh and processing markets. A reliable nondestructive method, which can distinguish affected and normal potatoes, is described here. A Varian 4.7 Tesla, 33-cm horizontal-bore spectroscopy/imaging system was used to obtain nuclear magnetic resonance (NMR) images of potatoes. A two-dimensional multi-slice spin-echo imaging technique was used to acquire the cross-sectional images along the longitudinal direction. The echo time was 35 msec and the repetition time was 1.2 sec. A total of 13 slice images were taken for each potato. A one-dimensional projection technique was also performed to evaluate the possibility of using fast-scan method. The brown center showed high intensity in long echo scans due to its longer TL relaxation time. A suberin-like layer resembling the periderm developed on the cavity wall of hollow heart causing a tan or dark brown coloration. This cavity wall also appeared in high intensity on the image. The affected potatoes can easily be sorted out using this nondestructive NMR imaging technique.

Length scales in heterogeneous polymers from solid state NMR

AbstractNew methods for probing structure and dynamics of heterogeneous polymers by multidimensional nuclear magnetic resonance (NMR) are described. On the molecular level high resolution multiple quantum spectroscopy of solids probes connectivities of different functional groups on length scales below 1 nm. On a mesoscopic scale NMR spin diffusion techniques probe phase separation and interfacial effects in polymer blends and block copolymers. On a macroscopic scale NMR imaging techniques allow to spatially resolve differences in order and mobility in the necking region or in shearbands of deformed polymers. The techniques are illustrated with amorphous polymers, elastomers, and core‐shell systems.

Diffusion of pyridine in Illinois No. 6 coal: measuring the swelling and deswelling characteristics by combined methods of nuclear magnetic resonance (NMR) and nuclear magnetic resonance imaging (NMRI)

The time-dependent swelling and deswelling of Illinois No. 6 coal by pyridine were measured by combined NMR and NMRI techniques. The results indicate that pyridine transport in this coal proceeds via Case II diffusion for swelling and via Fickian diffusion for deswelling. Once the relative pyridine concentrations reach values between 0.65 and 0.45, the coal's physical state changes from a glassy to a rubbery state. Transitions are well recorded by an inflection observed in the trend of spin-lattice relaxation or spin-spin relaxation of pyridine, as the coal swells and deswells. NMRI data indicate that the coal swelling is anisotropic, with swelling in a plane perpendicular to the coal bedding plane being 13% greater than that parallel to the coal bedding plane; however, the process of deswelling is almost isotropic. The differences between the swelling and deswelling characteristics are discussed from the viewpoint of coal's intrinsic structural properties and stored geologic pressure effects.

Industrial applications of nuclear magnetic resonance

Abstract During the past decade, the potential application of nuclear magnetic resonance (NMR) imaging techniques to industrial processing problems has been recognized. The particular strength of NMR is its ability to distinguish between chemical species and to yield information simultaneously on the structure, concentration distribution and flow processes occurring within a given process unit. In this paper, examples of specific applications are discussed including the study of (i) ceramics processing, (ii) the structure of polymeric materials and the application of polymers in controlled release technology, (iii) transport in porous media, (iv) transport in reactors, (v) food processing, and (vi) two-phase flow.

NMR parameter contrast in abundant-spin images of solids

Solid state nuclear magnetic resonance imaging (NMRI) techniques have been steadily improving over the years. Today high-resolution images of rigid solids are now accomplished by many different means. For abundant nuclei, the combination of multiple-pulse line narrowing and pulsed field gradients have greatly improved both the resolution and sensitivity of the imaging experiment, but often at the expense of the chemical information in the material. In this paper we discuss means of incorporating NMR parameters in the imaging experiment to generate image contrast which provides information about local variations in the chemistry of the material.

Applications of nuclear magnetic resonance imaging in process engineering

During the past decade, the application of nuclear magnetic resonance (NMR) imaging techniques to problems of relevance to the process industries has been identified. The particular strengths of NMR techniques are their ability to distinguish between different chemical species and to yield information simultaneously on the structure, concentration distribution and flow processes occurring within a given process unit. In this paper, examples of specific applications in the areas of materials and food processing, transport in reactors and two-phase flow are discussed. One specific study, that of the internal structure of a packed column, is considered in detail. This example is reported to illustrate the extent of new, quantitative information of generic importance to many processing operations that can be obtained using NMR imaging in combination with image analysis.

MRI investigations of fractures and multiphase flow in fractured media

AbstractThe new application of nuclear magnetic resonance imaging (MRI) techniques for characterizing fractures and flow in fractured media is investigated. Specifically, a relaxation‐weighted imaging technique is used for selectively highlighting either fracture or porous matrix regions. Many advantages over conventional spin‐density MRI techniques for characterizing fractured media are demonstrated. Its use to speed image acquisition is also demonstrated. In addition, a multislice profile imaging technique is used to investigate imbibition and drainage displacement experiments in fractured porous media. These images demonstrate that the fractures can have profound effects on the fluid distributions in multiphase flow.

Pattern Evolution of Granular Media Rotated in a Drum Mixer

ABSTRACTA homogeneous mixturea of different types of granular material will often segregate when rotated in a drum mixer. In the traditional axial segregation effect, the mixture of two different sizes of granular media will appear from the surface to separate into bands of relatively pure single concentrations along the axis of rotation. The initial pattern is not stable, but evolves in time with continued rotation through metastable states of fewer and fewer bands. We describe two experimental methods for measuring this evolution which provide a more complete picture of the dynamics involved in the pattern progression. The use of a CCD camera in conjunction with digital analysis techniques provides a consistent and precise measure of the state of the surface as a function of time. Nuclear Magnetic Resonance Imaging (MRI) techniques are used to noninvasively measure the segregation beneath the surface. These methods indicate that the underlying mechanisms of the pattern evolution originate in the bulk of the material beneath the avalanching surface.

Evolution of Regional Changes in Apparent Diffusion Coefficient during Focal Ischemia of Rat Brain: The Relationship of Quantitative Diffusion NMR Imaging to Reduction in Cerebral Blood Flow and Metabolic Disturbances

Middle cerebral artery occlusion was performed in rats while the animals were inside the nuclear magnetic resonance (NMR) tomograph. Successful occlusion was confirmed by the collapse of amplitude on an electrocorticogram. The ultrafast NMR imaging technique UFLARE was used to measure the apparent diffusion coefficient (ADC) immediately after the induction of cerebral ischemia. ADC values of normal cortex and caudate-putamen were 726 +/- 22 x 10(-6) mm2/s and 659 +/- 17 x 10(-6) mm2/s, respectively. Within minutes of occlusion, a large territory with reduced ADC became visible in the ipsilateral hemisphere. Over the 2 h observation period, this area grew continuously. Quantitative analysis of the ADC reduction in this region showed a gradual ADC decrease from the periphery to the core, the lowest ADC value amounting to about 60% of control. Two hours after the onset of occlusion, the regional distribution of ATP and tissue pH were determined with bioluminescence and fluorescence techniques, respectively. There was a depletion of ATP in the core of the ischemic territory (32 +/- 20% of the hemisphere) and an area of tissue acidosis (57 +/- 19% of the hemisphere) spreading beyond that of ATP depletion. Regional CBF (rCBF) was measured autoradiographically with the iodo[14C]antipyrine method. CBF gradually decreased from the periphery to the ischemic core, where it declined to values as low as 5 ml 100 g-1. When reductions in CBF and in ADC were matched to the corresponding areas of energy breakdown and of tissue acidosis, the region of energy depletion corresponded to a threshold in rCBF of 18 +/- 14 ml 100 g-1 min-1 and to an ADC reduction to 77 +/- 3% of control. Tissue acidosis corresponded to a flow value below 31 +/- 11 ml 100 g-1 min-1 and to an ADC value below 90 +/- 4% of control. Thus, the quantification of ADC in the ischemic territory allows the distinction between a core region with total breakdown of energy metabolism and a corona with normal energy balance but severe tissue acidosis.

Applications of Nuclear Magnetic Resonance Imaging in Particle Technology

AbstractDuring the past decade, the application of Nuclear Magnetic Resonance (NMR) imaging techniques to problems of relevance to the process industries has been identified. In the context of particle technology, NMR imaging, in addition to the more routinely used techniques of Pulsed Gradient Spin Echo (PGSE) NMR and NMR spectroscopy, offer new methods of characterising pore structure, adsorption and diffusion processes within particles and packed beds of particles, as well as enabling time‐resolved in‐situ study of processes such as twophase flow, aggregation, polymerisation, crystallisation and phase separation phenomena. This paper reviews recent work in these areas, and also highlights the new insights NMR imaging can give us regarding the characterisation of porous materials, and the influence of the structure of the pore space on the transport processes occuring within a given porous solid.

NMR imaging of polyethylene pipes

Abstract1H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two‐dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.

Industrial applications of nuclear magnetic resonance

During the past decade, the potential application of nuclear magnetic resonance (NMR) imaging techniques to industrial processing problems has been recognized. The particular strength of NMR is its ability to distinguish between chemical species and to yield information simultaneously on the structure, concentration distribution and flow processes occurring within a given process unit. In this paper, examples of specific applications are discussed including the study of (i) ceramics processing, (ii) the structure of polymeric materials and the application of polymers in controlled release technology, (iii) transport in porous media, (iv) transport in reactors, (v) food processing, and (vi) two-phase flow.

Dynamic Detection of a Phase Transition for Illinois No. 6 Coal in Pyridine by Nuclear Magnetic Resonance Imaging (NMRI) and NMR Spectroscopy

An Illinois No. 6 coal preswollen in pyridine was allowed to undergo slow deswelling by solvent evaporation. The process was monitored by NMR and NMRI techniques in order to better understand coal's macromolecular structure and mobility of solvent within the coal. Pyridine concentration profiles and spin-spin relaxation times measured by conventional 1 H NMR suggest that pyridine diffusion in the coal network during the initial stages of the deswelling process is Fickian and that the pyridine exists within two regimes of molecular mobility. NMR imaging perpendicular to and parallel to the coal bedding plane shows that the deswelling process follows nearly isotropic behavior. Once the pyridine concentration decreases to approximately 0.5 of the initial equilibrium concentration, a dramatic increase in the deswelling rate and decrease in pyridine concentration are observed, implying that a phase transition occurs at this point in the coal-pyridine system

Non-invasive imaging of fungal colonization and host response in the living sapwood of sycamore ( Acer pseudoplatanus L.) using nuclear magnetic resonance

Non-invasive nuclear magnetic resonance (NMR) imaging techniques revealed anatomical features of healthy sycamore ( Acer pseudoplatanus L.) stems, the pathological anatomy of sooty bark disease [ Cryptoslroma corticale (Ell. and Everh.) Gregory & Waller] lesions, and the dynamics of fungal invasion and host response in excised lengths of living sycamore stems challenged with Ustulina deusta (Fr.) Petrak or Chondroslereum purpureum (Pers. ex Fr.) Pouz. Infected wood and reaction zones could be distinguished clearly from healthy tissue in these images. Lesion development, observed by the sequential imaging of individual stems, followed the course deduced from the destructive examination of a set of similar stem lengths. U. deusta was unable to penetrate far into the living stem lengths, and responses chemically and morphologically similar to the reaction zones formed at the margins of naturally occurring decay lesions were expressed at the interface between healthy and colonized xylem. In contrast C. purpureum rapidly invaded and killed excised stem lengths with little or no induction of characteristic reaction zone responses. Calculated proton density ( M o ) images indicated that water levels in the reaction zones delimiting U. deusta lesions were elevated by a factor of approximately 2·5–3·0. No such accumulation of water occurred at the margin of C. purpureum lesions. The significance of this in relation to xylem defence against fungal attack is discussed.

Nuclear Magnetic Resonance Detection of the Consequences of Transgene Expression

Physiological processes can be altered in a very specific manner using transgenic mouse techniques. Physiological processes can be noninvasively monitored using nuclear magnetic resonance imaging and spectroscopic techniques. Three illustrations of the combination of these two rapidly developing techniques to study neuronal function, energy metabolism, and sickle cell anemia are discussed.