Thesis submitted in accordance with the requirements of the University of Liverpool for the degree of Doctor in Philosophy by Michael J. Puddephat, B.Sc. M.Sc. May, 1999

This thesis is the result of my own work. The material contained in the thesis has not been presented, nor is currently being presented, either wholly or in part for any other degree or qualification. The research work was carried out at the Magnetic Resonance and Image Analysis Research Centre, University of Liverpool.