| Autor: |
E.W.G. Jones, S.J. Gibbs, Laurance D. Hall, J.A. Derbyshire, M. Peyron, Alun J. Lucas |
| Rok vydání: |
1993 |
| Předmět: |
|
| Zdroj: |
Journal of Magnetic Resonance, Series A. 104:273-282 |
| ISSN: |
1064-1858 |
| DOI: |
10.1006/jmra.1993.1224 |
| Popis: |
Problems associated with large, static magnetic-field gradients are reviewed and illustrated with pulsed-field-gradient NMR diffusion-imaging experiments on two model systems. The model systems chosen are a water-filled cylinder and a water-filled annulus between two concentric cylinders both oriented transversely to the polarizing magnetic field. The latter system exhibits large magnetic-field gradients (∼5 G cm −1 ), and the simplicity of the geometry permits an analytical description of the magnetic-field distribution in the sample; calculations of the field distribution are consistent with direct measurements made using the chemical-shift-imaging technique. Diffusion-imaging experiments based on either spin- or stimulated-echo sequences are reliable for the single-tube system in which static gradients are negligible. However, for the double-tube system, the large static gradients prevent reliable diffusion imaging by spin-echo methods and cause artifacts in the results of standard stimulated-echo techniques. A superior alternating-pulsed-field-gradient technique, for which echo attenuation is less sensitive to the effects of the static background magnetic-field gradients, provides reliable diffusion-coefficient images for the double-tube system. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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