Effects of dipolar fields in NMR and MRI.
Year: 2004
Type: dissertation
Abstract: The work presented in this thesis was undertaken by the author, except where it is indicated by reference, within the Sir Peter Mansfield Magnetic Resonance Centre at the University of Nottingham during the period July 2001 until November 2004. The initial objective of the PhD was to investigate possible applications of long range dipolar field effects, but other problems involving the effects of susceptibility induced magnetisation have also been discussed. The work on the long range dipolar field involved: • The study of the evolution at high field of the various orders of quantum coherences and 2D spectroscopy experiments based on long range dipolar fields; • The optimisation of parameters for imaging with the double quantum CRAZED sequence and derivation of phase cycles that allow the elimination of undesired signals such as stimulated echoes and refocused spin echoes; • Simulations of the effects of field inhomogeneities on the long range dipolar field and signal evolution after a double quantum CRAZED sequence; The work relating to the fields generated by susceptibility induced magnetisation involved: • Application of a methodology originally derived for evaluating the long range dipolar field to the rapid calculation of field inhomogeneities due to induced magnetisation (dipoles). Studies were performed using a digitised body model. The effect of head movement and breathing were simulated allowing the evaluation of the consequences of these inhomogeneities for imaging; • The methodology referred above was used to compare the BOLD contrast, due to both the intra and extra-vascular compartments, resulting from infinite cylinders and a realistic vascular model (based on the rat cortex); • Development of a methodology for monitoring variation of field inhomogeneities with movement in functional studies, that can be used to apply an undistortion for each echo planar image acquired.
Authors: R. Ferreira‐Marques, JoseÌ Pedro.
Language: English
Subfield: Radiology, Nuclear Medicine and Imaging
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2133206777