Many of the problems faced in magnetic resonance imaging and angiography are due to hardware limitations of the scanners used. The use of multidimensional excitation pulses, and new, fast acquisition sequences such as echo-planar and spiral imaging, put demands on the gradient systems and although technology is progressing in these areas, performance must be carefully monitored to ensure artefact-free images. This thesis deals with four distinct aspects of magnetic resonance imaging (MRI). / A simple hardware modification to decrease the minimum achievable echo-time of our MRI scanner was designed, built, programmed and tested and was found to improve the quality of inflow angiograms significantly. Further improvements were demonstrated with the use of on-resonance (binomial) magnetization transfer saturation contrast enhancement pulses. / A method for measuring the k-space trajectories of gradient waveforms was adopted, modified, validated and used to measure the k-space trajectories of gradient waveforms used for selective excitation and spiral image acquisition. Distortion was observed even when gradient waveforms were designed within specifications of the manufacturer. / The literature reports the application of the k-space model, usually associated with image acquisition, to the design of multidimensional selective excitation pulses. This thesis demonstrates theoretically and experimentally the modification of the design procedure to compensate RF envelopes for distortion of the k-space trajectories of the accompanying gradient waveforms by using measured k-space data. / The correction of spiral image reconstruction algorithms to compensate for k-space trajectory distortion was also demonstrated theoretically and experimentally.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.28930 |
| Date | January 1995 |
| Creators | Takahashi, Atsushi M. (Atsushi Mark) |
| Contributors | Peters, T. M. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biomedical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001441010, proquestno: NN05798, Theses scanned by UMI/ProQuest. |
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