Biomedical subjects

L F Gladden

Publications and source records attributed to L F Gladden.

At least 19 recordsLinked to original sources

PubMed2006

Real-time measurement of bubbling phenomena in a three-dimensional gas-fluidized bed using ultrafast magnetic resonance imaging.

Ultrafast magnetic resonance imaging has been applied for the first time to measure simultaneously both the rise velocities and coalescence of bubbles, and the dynamics of the solid phase in a gas-solid two-phase flow. Here, we consider the hydrodynamics within a gas-fluidized bed of particles of diameter 0.5 mm contained within a column of internal diameter 50 mm; gas velocities in the range of 0.18-0.54 m/s were studied. The data are of sufficient temporal and spatial resolution that bubble size and the evolution of bubble size and velocity following coalescence events are determined.

Journal Article↗

PubMed2004

Fast emulsion droplet sizing using NMR self-diffusion measurements.

Emulsion droplet sizing using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) is a well-established technique. Traditionally these measurements require total acquisition times of typically 5-20 min per sample, which severely limits our ability to use this method to study dynamic processes. Here we present the application and verification of an NMR pulse sequence, Difftrain, which enables emulsion droplet size distributions to be measured in 3-10 s. We have previously introduced applications of Difftrain (C. Buckley, K.G. Hollingsworth, A.J. Sederman, D.J. Holland, M.L. Johns, L.F. Gladden, J. Magn. Reson. 161 (2003) 112-117), including the droplet sizing of a single unimodal emulsion sample. In this paper, several model emulsions containing different oils are measured and the results compared directly with sizing provided by laser scattering. In this manner, the Difftrain method is verified and its possibilities and limitations are explored. Guidelines are proposed for the range of droplet sizes for which accurate results can be produced. The Difftrain technique opens up the possibility of studying non-equilibrium emulsions; a study of the in situ emulsification of a 21% v/v water-in-silicone oil emulsion is presented.

Journal Article↗

PubMed2004

Quantitative magnetic resonance imaging of urea and lysozyme in protein chromatography.

Magnetic resonance imaging (MRI) techniques have been implemented to enable quantitative imaging of protein and urea within a 5 ml HiTrap size-exclusion chromatography desalting column, without introduction of contrast agents. One-, two- and three-dimensional images of urea injected at concentrations of 2, 4, 6 and 8 M were acquired. One-dimensional profiles of lysozyme at concentrations between 5 and 25 mg ml(-1) were also obtained. All data were accurate to within +/- 15% when compared to the known amount injected. Quantitative MRI elution profiles of both urea and lysozyme were then obtained in real-time during a desalting separation.

Magnetic Resonance Imaging↗

PubMed2004

Development and application of rotationally compensated RARE.

In this paper we describe a new extension to the RARE rapid imaging technique--ROTACOR--which compensates for constant sample rotational motion by rotating the direction of the gradient coordinate system (read and phase directions) between each refocusing RF pulse and therefore between each acquisition of a line of k-space in the read direction. In the laboratory frame this corresponds to an irregularly sampled k-space raster; for a sample rotating at the predefined rotation rate this will correspond to the sampling of a rectilinear k-space raster. This technique is applied to two rotating systems. First, to demonstrate the technique, a rotating mixing paddle in water is imaged using conventional RARE and then using the ROTACOR sequence, demonstrating the improvement of image quality produced by ROTACOR. Second, ROTACOR is used to image the deformation of water droplets in silicone oil, being sheared in a wide-gap Couette cell. Accurate imaging of the droplet shape as a function of shear rate, permits determination of the interfacial tension between the two fluids concerned; the results compare favourably with reported literature values.

Journal Article↗

PubMed2003

Single excitation multiple image RARE (SEMI-RARE): ultra-fast imaging of static and flowing systems.

This paper describes the development and application of a new rapid, full k-space acquisition imaging pulse sequence based on the rapid acquisition with relaxation enhancement (RARE) methodology. We have termed this pulse sequence single excitation multiple image RARE (SEMI-RARE). We demonstrate the application of SEMI-RARE to the visualisation of a static liquid phantom and it is shown that up to 120 images can be acquired from a single excitation. By exploiting the inherent relaxation and diffusion contrast within the series of images, the SEMI-RARE provides an ultra-fast method for characterising the spatial distribution of chemical species and phases within complex systems. The pulse sequence is then applied to the study of single- and two-phase flow in a single narrow tube of inner diameter 2.9mm. In particular, it is shown that 8 two-dimensional slice-selective images for two-phase bubble-train flow in a single tube can be acquired from a single excitation at effective echo-times of 37, 109, 181, 253, 325, 397, 469, and 541ms. The visualisation enables the determination of gas/liquid bubble sizes and velocities during two-phase flow. We also report the first direct evidence, obtained from magnetic resonance measurements, of liquid re-circulation zones associated with bubble-train flow. The robustness of the SEMI-RARE technique makes it an attractive fast imaging technique for the study of multi-phase flow phenomena, which are often characterised by large variations in magnetic susceptibility, and are of widespread interest in chemical engineering.

Journal Article↗

PubMed2003

Applications of fast diffusion measurement using Difftrain.

Novel applications of fast self-diffusion measurement are presented. Difftrain (Diffusion train), which uses successive stimulated echoes from a single excitation pulse where a portion of the available magnetisation is recovered for each echo, is used to measure self-diffusion by varying the observation time. It is applied to produce the droplet size distribution of an oil-in-water emulsion in less than 4s. This is verified by comparison with the droplet size distribution produced by a standard pulsed field gradient (PFG) technique. Difftrain is also extended to enable the application of incremental gradients, in addition to varying the observation time. This is used to produce propagators or displacement probabilities of water flowing through a packed bed for a range of 16 observation times in under 10 min. Again verification is provided by acquisition of the same propagators using a conventional PFG technique.

Journal Article↗

PubMed2002

Sizing of emulsion droplets under flow using flow-compensating NMR-PFG techniques.

Using the nuclear magnetic resonance (NMR) pulsed field gradient (PFG) technique, it is possible to determine the size distribution of emulsion droplets. This method is extended so that the same measurements can be performed in the presence of flow. The resultant flow-compensating NMR-PFG technique is used to determine the oil droplet-size distribution of an oil-in-water emulsion flowing in a narrow tube at various flow rates. Comparison with the nonflowing oil droplet-size distribution enables the effect of velocity shear on the oil droplet-size distribution to be quantified.

Emulsions↗

PubMed1999

Measuring water distribution in extrudates using magnetic resonance imaging (MRI).

Magnetic resonance imaging (MRI) has been applied to the evaluation of the distribution of water in extrudates produced by extruding pastes. Two model drugs similar in chemical structure were mixed with microcrystalline cellulose (MCC) and with two different amounts of water and extruded at two different extrusion speeds using a ram extruder. Extrudates were collected during the steady-state stage of the extrusion profile and were analysed for the water distribution using MRI. The percolation threshold for each sample was calculated to evaluate the degree of water structure within the sample. The water distribution inside the extrudates was surprisingly uniform. The extrudates produced using the faster extrusion speed had a significant lower percolation threshold, which suggests the existence of a greater water structure in the extrudates. A significant correlation was found between the percolation threshold and the extrusion force, which had been used to provide the extrudates.

Chemistry, Pharmaceutical↗

PubMed1996

Structure-transport relationships in porous media.

An understanding of adsorption, transport, and reaction processes occurring within porous materials is central to the design and optimisation of chemical processing operations such as gas separations, catalysis, and soil remediation. To address many of the important questions in these areas the process engineer needs to characterise heterogeneities in both the physical and chemical properties of porous media, and to identify the importance of these properties in determining the operating characteristics of the system under consideration. In this paper three examples, each considering different types of structure-transport correlation, are discussed: (1) single and binary component adsorption processes in zeolites, (2) structure and transport heterogeneity in porous catalyst pellets, and (3) the characterisation of the interparticle space in packed beds of particles.

Magnetic Resonance Imaging↗

PubMed1994

Probing the structure of porous pellets: an NMR study of drying.

Partially saturated porous catalyst support pellets have been studied using NMR relaxation, PGSE, and imaging techniques. Spatially nonresolved PGSE data were acquired as a function of the fractional saturation of the pellets during drying. Combination of these data with an estimate of the width of the pore-size distribution, as determined by mercury porosimetry, and the results of numerical simulations of diffusion in a random pore network enabled predictions of the connectivity of the pore structure to be determined. NMR imaging was shown to be effective in discriminating between different models of drying; even when the bulk drying curves are similar, significantly different moisture redistribution phenomena are seen to occur.

Desiccation↗

PubMedDate not supplied

Magnetic resonance visualisation of single- and two-phase flow in porous media.

Three-dimensional MRI and flow visualisation data are presented for single and two-phase flow occurring within packed beds of glass spheres. The initial motivation for this work has been to understand the operation of fixed-bed reactors used in many chemical processing operations; these systems also serve as model porous media in which to investigate the effect of the structure of a pore space on the flow phenomena occurring within it. For the case of single-phase flow, maps of the liquid shear rate components are calculated from which forces on individual spheres within the bed are obtained. The velocity histogram for flow transverse to the direction of superficial flow is exponential in both negative and positive directions. This form of the velocity histogram implies an exponential form for the displacement propagator, in contrast to the Gaussian distribution obtained by pulsed gradient spin echo measurements. This difference arises because the spatially resolved velocity imaging sequence measures only the average velocity within each voxel and is insensitive to the effects of incoherent (diffusive) motion. Visualisations of air-water flow through a sphere pack are also reported and the capability of MRI to yield information on rivulet formation and surface wetting characteristics is illustrated.

Glass↗

PubMedDate not supplied

MRI investigation of hydration and heterogeneous degradation of aliphatic polyesters derived from lactic and glycolic acids: a controlled drug delivery device.

Magnetic Resonance Imaging experiments have been used to investigate the degradation of drug-loaded poly(glycolic lactic acid) (PGLA) 50:50 cylinders. Spatial variation in the rate of degradation throughout the polymer cross-section has been observed non-invasively using quantitative imaging of penetrant concentration, T(2) and self-diffusion coefficient. This spatial variation in the rate of degradation was attributed to the quicker degradation in the inner region of the sample due to autocatalysis by carboxyl end groups generated upon ester bond cleavage.

Catalysis↗

PubMedDate not supplied

MRI velocimetry and lattice-Boltzmann simulations of viscous flow of a Newtonian liquid through a dual porosity fibre array.

Viscous flow through fibrous porous media has considerable importance in a number of industrial processes including, in particular, resin transfer molding. In this paper magnetic resonance flow imaging techniques are used to visualize flow of a Newtonian liquid through a dual porosity structure. Of particular interest in these studies is the transition in the flow as the liquid moves from the open region into the fiber array. The ability of lattice-Boltzmann simulations to predict the visualized flow fields is presented and discussed.

Computer Simulation↗

PubMedDate not supplied

MRI as a probe of the deposition of solid fines in a porous medium.

MRI volume imaging and flow visualizations are used to investigate solid fine-particle deposition during flow within a random packing of glass spheres. This process is of importance in many fields including filtration, operation of chemical reactors and oil recovery. Visualizations before and during deposition allow us to investigate how the structure of the inter-particle space and the properties of the fines influence the evolution of the structure and hydrodynamics characterizing the porous medium during deposition.

Filtration↗

PubMedDate not supplied

In situ magnetic resonance measurement of conversion, hydrodynamics and mass transfer during single- and two-phase flow in fixed-bed reactors.

In recent years there has been increasing interest in applying magnetic resonance (MR) techniques in areas of engineering and chemical technology. The science that underpins many of these applications is the physics and chemistry of transport and reaction processes in porous materials. Key to the exploitation of MR methods will be our ability to demonstrate that MR yields information that cannot be obtained using conventional measurement techniques in engineering research. This article describes two case studies that highlight the power of MR to give new insights to chemical engineers. First, we demonstrate the application of MR techniques to explore both mass transfer and chemical conversion in situ within a fixed bed of catalyst, and we then use these data to identify the rate-controlling step of the chemical conversion. Second, we implement a rapid imaging technique to study the stability of the gas-liquid distribution in the low- and high-interaction two-phase flow regimes in a trickle-bed reactor.

Acetic Acid↗

PubMedDate not supplied

Quantitative 'real-time' imaging of multi-phase flow in ceramic monoliths.

An extension of the RARE technique has been developed which acquires multiple images from a single radio-frequency excitation. This pulse sequence has been used to image, in real-time, gas flow through stagnant liquid within parallel-channel ceramic monoliths. From these images, gas-phase volume fractions, and distributions of gas bubble length and velocity as a function of gas flow rate (50-300 cm3 min(-1)) and channel size (300 and 400 channels per square inch, cpsi) are obtained directly. Increasing the gas flow rate increased the number of large bubbles and the average bubble velocity. A bimodal distribution in the bubble velocities was observed for flow within the larger channel size (300 cpsi) in contrast to a broad unimodal distribution characterizing two-phase flow within the smaller channel size (400 cpsi).

Ceramics↗

PubMedDate not supplied

Magnetic resonance imaging study of complex fluid flow in porous media: flow patterns and quantitative saturation profiling of amphiphilic fracturing fluid displacement in sandstone cores.

Magnetic resonance imaging is used to follow the removal process of a visco-elastic surfactant (VES) fracturing fluid in Bentheimer sandstone cores at typical reservoir temperatures (T=333 K). Two displacing fluids were investigated, a Gadolinium doped water phase (1M NaCl solution), and a Gadolinium doped hydrocarbon phase (Mineral Spirits). In addition to flow characteristics obtained by conventional core-flooding, i.e., the macroscopically averaged volumetric flow rates and differential pressures, we have also measured the saturation profiles and characteristic displacement patterns during all stages of the removal process. To acquire these data we have used quantitative one-dimensional chemically specific profiling along with fast two-dimensional imaging experiments while flooding Bentheimer sandstone cores in situ in the spectrometer. Our results show that both displacement processes (complex fluid displaced by water or hydrocarbon phase) are dominated by the large viscosity contrasts present. However, distinct differences were found between the displacement characteristics of water and hydrocarbon, which confirmed the sensitivity of the complex fracturing fluid to the displacing fluid.

Gadolinium↗

PubMedDate not supplied

Magnetic resonance studies of dissolving particulate solids.

Magnetic resonance methods have been used to elucidate the internal pore structure of particulate solids, in particular detergent tablets. Such information is essential to a comprehensive understanding of the dissolution characteristics of these materials and how this property is related to processing conditions during tablet formation. In particular 3-D images of porosity are produced and 2-D self-diffusion maps are acquired as a function of observation time, which enables pore size to be quantified as a function of position via the extracted surface-to-volume ratio of the pore space. These properties are determined as a function of processing parameters, in particular the compression force used in tablet formation.

Detergents↗