Despite the vast myriad of applications and the long way it has come, MRI is still a relatively new field of knowledge with much prospect for more advancement and expansion. This work is mainly concerned with two gradient echo imaging methods which are directly or indirectly related to blood vessel imaging as well as iron depiction in the human brain. In each case, new methods are introduced that overcome existing limitations.
For blood vessel imaging, 3D Time-of-Flight (TOF) MR angiography (MRA) with its known capability to image arteries as well as veins was implemented at 3.0 T. At this field strength, the significant RF profile variability due to RF inhomogeneity is a liability for circle-of-Willis imaging in the human brain that was overcome by introducing a new means to counter the RF effects through increased slope of the ramped pulse. In addition a new method is introduced for TOF MRA with two-in-one arterial and venous 3D TOF imaging to overcome the significant scan time overhead of a traditional second venous scan and for cutting down RF power utilization. Using this method, total scan time could be reduced by as much as 46% and specific absorption rate (SAR) due to spatial saturation could be reduced by as much as 92%.
For iron sensitive imaging, Susceptibility Weighted Imaging (SWI) was developed at 4.7 T. The phase SWI method was used to visualize lesions in Multiple Sclerosis (MS) patients and was experimentally compared to the visibility on standard T2 weighting with results demonstrating visualization of new lesions, with 18% of total lesions exclusively visible on SWI.
A new approach to 3D imaging was also introduced to enable accurate oblique SWI scanning while overcoming the current restriction to axial imaging to produce correct phase effects for oblique imaging. New results from oblique phase imaging were presented and the phase measurements from key brain structures were successfully validated against images obtained by the current standard of axial imaging.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.10048/1131 |
| Date | 06 1900 |
| Creators | Eissa, Amir |
| Contributors | Alan Wilman (Biomedical Engineering), Frances Fenrich (Physics), Alan Wilman (Biomedical Engineering), Frances Fenrich (Physics), Jack Tuszynski (Physics), Nicola De Zanche (Oncology), Richard Frayne (Radiology and Clinical Neurosciences; University of Calgary) |
| 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 | Thesis |
| Format | 5306102 bytes, application/pdf |
| Relation | Eissa, A; Lebel, RM; Korzan, JR, et al. Detecting Lesions in Multiple Sclerosis at 4.7 Tesla Using Phase Susceptibility-Weighting and T2-Weighting. JMRI 30(4): 737-742, 2009., Eissa, AM; Wilman, AH. Effects of RF inhomogeneity at 3.0T on ramped RF excitation: Application to 3D time-of-flight MR angiography of the intracranial arteries. JMRI 25(3) 466-472, 2007. Wiley-Liss, Inc. && Conference Information: 12th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine, Date: MAY 15-21, 2004 Kyoto JAPAN, Eissa, A; Wilman, AH. Simultaneous and Time Efficient Arterial and Venous Time of Flight MRA with Reduced RF Power. 17th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine, 2009., Eissa, A; Wilman, AH. 3D MRI with Independent Excitation and Acquisition Volumes: Application to Oblique SWI. Report of invention with the University of Alberta, Provisional Patent has been filed. |
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