Acute ischemic events associated with atherosclerosis are most often caused by rupture or erosion of unstable plaques. Clinical studies have demonstrated that in-vivo multi- contrast MRI can characterize plaque morphology and composition to evaluate the vulnerability of atherosclerotic plaques. The standard protocol for carotid imaging uses the Double-Inversion-Recovery (DIR) Fast-Spin-Echo (FSE) pulse sequence to acquire black-blood 2D high-resolution cross-sectional T\W, PDW and T2W images. With the addition of bright-blood Time-of-Flight images, it was demonstrated that in-vivo multi- contrast MRI could discriminate the major plaque components: lipid-rich necrotic core, intra-plaque haemorrhage, fibrous tissue and calcification. Given the nature and the large amount of multi-contrast MRI data, clinical studies of atherosclerosis would benefit from the availability of reliable and accurate automated techniques for image registration, segmentation and plaque classification. Recent multi-contrast MRI studies presented automatic plaque characterization methods that showed promising results under ex-vivo and in-vivo conditions. This thesis investigates some weaknesses in the current image acquisition and analysis techniques, which can affect the results of in- vivo MRI plaque characterization, and then proposes novel methods to advance the understanding of atherosclerosis in the carotid arteries. An automated multi -contrast registration algorithm that corrects for misalignments between carotid images caused by patient motion using sub-pixel accuracy and different similarity metrics was developed and validated. This project also used an alternative in-vivo carotid imaging approach based on the DIR Multi-Echo-Spin-Echo (Multi-SE) pulse sequence that acquired a series of black-blood 2D high-resolution cross-sectional images at different echo times. Quantitative T2 maps and synthetic multi-contrast images of carotid arteries were calculated from the Multi-SE images. T2 maps were automatically segmented and classified to provide in-vivo T2 measurements of the main plaque components, while Multi-SE synthetic images were compared with FSE images to demonstrate that the FSE acquisition strategy causes a significant loss of vessel edge sharpness.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558196 |
| Date | January 2011 |
| Creators | Biasiolli, Luca |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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