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Anisotropic diffusion weighted contrast in magnetic resonance images of the human subject

Doran, Mark; (1994) Anisotropic diffusion weighted contrast in magnetic resonance images of the human subject. Doctoral thesis (M.D), UCL (University College London). Green open access

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Abstract

The proton nuclear magnetic resonance signal of biological systems arises mainly from water. Its intensity is time dependent and varies with a number of physical properties of water. The resulting contrast (or signal difference between two tissues) displayed in an image varies with the proton density, the relaxation times T1 and T2 of the tissues as well as the mobility of the protons. This thesis considers the clinical development of the use of the pulsed gradient spin echo (PGSE) sequence, designed to detect microscopic molecular motion. However motion sensitization itself leads to grave practical difficulties with image artefact. Motion artefact suppression methods are discussed in detail. Despite the difficulties, it was possible to produce images that represented the relative mobility of water in differing defined directions i.e. directional contrast. Application of this imaging technique to normal subjects allowed direct visualisation of the fibre tracts within the white matter. Evidence is advanced to support the contention that directional contrast arises from the properties of the myelin sheath. Small scale studies of different diseases were undertaken to assess the type of change that might be expected with this type of imaging. It is shown that some anisotropy of lesions is detectable in multiple sclerosis, an effect not evident in other pathologies such as infection and stroke. Tumours with their surrounding oedema showed marked changes in the appearance when imaged with this method. It is concluded that diffusion weighted imaging will have a role in clinical practice as a method to increase the specificity of magnetic resonance as an imaging technique. However the practical problems of motion artefact control need to be much improved before routine application is possible.

Type: Thesis (Doctoral)
Qualification: M.D
Title: Anisotropic diffusion weighted contrast in magnetic resonance images of the human subject
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Health and environmental sciences; Diffusion weighted imaging
URI: https://discovery.ucl.ac.uk/id/eprint/10102618
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