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od 2020-09-20 |
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1. |
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Transverse gradient coil with circle current paths The paper describes a new type of transverse magnetic field gradient coil for applications in MRI and MRS. It uses full circle current paths rather than current arcs and has a particularly simple unit construction of symmetric form. It features a large volume of uniform transverse field gradient, high efficiency and low inductance for rapid switching. A prototype coil has been constructed and evaluated to check computer simulations. Two smaller sets have subsequently been made for NMR microscopy. This coil design may be used for all sizes.
(C) 1998 Elsevier Science BV. All rights reserved. |
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Magnetic Resonance Materials in Physics, Biology and Medicine - MAGMA, 7(1), 55-60, (1998) |
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2. |
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Molecular motion in solid all-trans retinoic acid (vitamin A acid) by proton NMR An investigation of the molecular dynamics of all-trans retinoic acid (vitamin A) has been carried out in the solid state by proton NMR. Measurements were made of T-1 at 14 and 25 MHz and of second moment at 25 MHz in the temperature range 55 to 420 K for both monoclinic and triclinic forms. In the monoclinic state relaxation was attributed to methyl group reorientation below 250 K and to conformational motion of the cyclohexene ring above this temperature. Activation energies and time constants were derived for the motions. In the triclinic state the same motions were active, but the cyclohexene ring motion was less restricted and some of the methyl group motions were more restricted indicating that hindrances to the motions were at least partly determined by the intermolecular packing arrangements.
(C) 1998 Elsevier Science B.V. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 13(1-2), 39-43, (1998) |
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3. |
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13C NMR relaxation in supercooled di-methyl phthalate Spin-lattice relaxation times (T-1) and nuclear Overhauser enhancement factors (NOE) for the individual ring carbons in di-methyl phthalate (DMF) were measured over a wide range of temperatures. The results show that the reorientational correlation function corresponding to the global dynamics in supercooled liquid can be well described by a Davidson-Cole distribution. The viscosity dependence of the reorientational correlation time tau derived is analysed to investigate the adequacy of the modified Debye equation to description of the microscopic behaviour of supercooled systems.
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Journal of Physics-Condensed Matter, 10(28), 6243-6249, (1998) |
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4. |
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Molecular dynamics in solid L-adrenaline by proton NMR Proton NMR measurements of the spectrum, second moment, spin-lattice relaxation time T-1 and dipolar relaxation time T-1D were carried out on polycrystalline L-adrenaline at 14 and 25 MHz between 55 and 400 K. Between 70 K and 250 K relaxation is dominated by C-3 reorientation of the single methyl group in each molecule, characterized by an activation energy 8.3 ± 0.3 kJ/mole. Below 70 K tunnelling assisted relaxation is significant, characterized by an excitation energy of 1.9 ± 0.2 kT/mole. Above 250 K an additional molecular motion becomes significant, with activation energy above 28 kT/mole, attributed to conformational motion of the methylene group in the ethylamine side chain.
(C) 1998 Elsevier Science B.V. |
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Solid State Nuclear Magnetic Resonance, 10(3), 117-121, (1998) |
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5. |
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Novel gradient coils for magnetic resonance microscopy This paper describes three magnetic field gradient coils of considerable simplicity, two for transverse gradient and one for longitudinal gradients.
The coaxial arc gradient coil has a simple unit construction of symmetric form. It features a large volume of uniform transverse field gradient, high efficiency and low inductance rapid switching. A prototype coil was first constructed and a smaller coil set was [hen constructed for NMR microscopy, with excellent results. The system may be used for all sizes from microimaging to whole-body MRI.
The second transverse gradient coil uses full circle current paths rather than current arcs. It has an even simpler form of construction and has closely similar properties to the coaxial arc transverse gradient coil. A prototype coil set was first made and two smaller coil sets have been made for NMR. microscopy.
The longitudinal gradient coil is based on an analysis of the multipole expansion of the external field of a gradient coil system. It is first shown that a Maxwell pair has no hexadecapole moment. The field outside such a pair therefore falls as r-4 from the quad-rupole moment and as r-8 from the 64-pole moment. Using a nested pair of Maxwell pairs the quadrupole term is canceled leaving only the rapid attenuation of the r-8 term, thus providing a simple screened Longitudinal gradient coil.
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Spatially Resolved Magnetic Resonance, Eds. Blumler P., Blumich B., Botto R., Fukushima E., WILEY-VCH, Weinheim, New York, Chichester, Brisbane, Singapore, Toronto, 683-693, (1998) |
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