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Biomedical subjects

D G Cory

Publications and source records attributed to D G Cory.

42 records · Page 3Linked to original sources
PubMed1997

Nuclear magnetic resonance imaging of solid rocket propellants at 14.1 T.

Proton NMR images of solid propellant materials, consisting of a polybutadiene binder material filled with 82% solid particles, have been obtained at a magnetic field strength of 14.1 T and at a resolution of 8.5 x 8.5 micron. The images are the first of elastomeric materials obtained at a proton frequency of 600 MHz and have the highest spatial resolution yet reported. The images display a high contrast and are rich in information content. They reveal the distribution of individual filler particles in the polymer matrix as well as a thin polymer film of about 10-30 micron which is found to surround some of the larger filler particles.

Fossil Fuels↗
PubMed1996

Distortions in multiple-pulse solid state NMR imaging: gradient decoupling, time-sequenced second averaging, and over-sampling.

Three approaches to reducing image artifacts are described that are specific to multiple-pulse line-narrowing methods of NMR imaging. Gradient decoupling avoids excess line broadening from off-resonance gradient phase evolution by restricting the gradient to selected windows in which the gradient Hamilton an commutes with the toggling frame state, and where the averaged Hamiltonian between gradient pulses is either cyclic or anti-cyclic. This forces the residual averaged dipolar Hamiltonian to be independent of the gradient evolution. Time-sequenced second averaging addresses the on-resonance broadening, where residual error terms dominate the spin dynamics (a lack of second averaging), by adding a second coherent averaging that retains part of the modulation associated with off-resonance terms, and thus smoothes out the line-narrowing efficiency with spatial offset. Over-sampling is useful to increase both the resolution and sensitivity of an image, but it introduces a sampling modulation that produces sidebands. These are eliminated by a series of prepulses in a fashion reminiscent of CYCLOPS phase cycling.

Magnetic Resonance Spectroscopy↗
PubMed1992

Multiple pulse NMR imaging of polymers and chemistry.

Multiple pulse line narrowing techniques can be used to improve resolution and sensitivity in solid state NMR imaging. For example, pulse sequences which remove homonuclear dipolar broadening have been used to image proton-containing materials. Further enhancements in resolution and sensitivity are obtained by removing inhomogeneous interactions such as chemical shift, susceptibility, and heteronuclear dipolar broadening. Pulse sequences have been designed which provide efficient line narrowing over large spectral widths by taking into account the experimenter's control over the amplitude and time dependence of the gradient-induced resonance offset. These methods have been applied to centimeter sized samples to obtain images of polymers, composite materials, and gas-solid chemical reactions. T1 and T2 contrast allows differentiation between materials.

Magnetic Resonance Spectroscopy↗
PubMed1990

Measurement of translational displacement probabilities by NMR: an indicator of compartmentation.

We introduce and demonstrate an NMR pulsed gradient stimulated echo method of directly obtaining the molecular translational displacement probability (displacement profile) of a liquid. The temporal development of the displacement profile reflects the presence of diffusion, restrictions to diffusion (e.g., walls, membranes), flow, and spatially dependent relaxation sinks. This approach allows the study of compartments which are too small to be observed by conventional NMR imaging methods. The distribution of spatial properties of compartments can be characterized over a spatial field of about 0.1 to 25 microns, completely independent of the absolute spatial location of the individual compartments.

Dimethyl Sulfoxide↗
PubMedDate not supplied

Applications of controlled-flow laser-polarized xenon gas to porous and granular media study.

We report initial NMR studies of continuous flow laser-polarized xenon gas, both in unrestricted tubing, and in a model porous media. The study uses Pulsed Gradient Spin Echo-based techniques in the gas-phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients. Pulsed Gradient Echo studies of continuous flow laser-polarized xenon gas in unrestricted tubing indicate clear diffraction minima resulting from a wide distribution of velocities in the flow field. The maximum velocity experienced in the flow can be calculated from this minimum, and is seen to agree with the information from the complete velocity spectrum, or motion propagator, as well as previously published images. The susceptibility of gas flows to parameters such as gas mixture content, and hence viscosity, are observed in experiments aimed at identifying clear structural features from echo attenuation plots of gas flow in porous media. Gas-phase NMR scattering, or position correlation flow-diffraction, previously clearly seen in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack is not so clear in experiments using a different gas mixture. A propagator analysis shows most gas in the sample remains close to static, while a small portion moves through a presumably near-unimpeded path at high velocities.

Diffusion↗