Diffusion Imaging in the Presence of Static Magnetic-Field Gradients

• Published in: Journal of magnetic resonance. Series A 1993-10, Vol.104 (3), p.273-282
• Main Authors: Lucas, A.J., Gibbs, S.J., Jones, E.W.G., Peyron, M., Derbyshire, J.A., Hall, L.D.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Infrared, submillimeter wave, microwave and radiowave instruments, equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipments and techniques
• ISSN: 1064-1858; 1096-0864
• DOI: 10.1006/jmra.1993.1224

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.