Atherosclerotic plaque (AP) composition is an important factor influencing plaque rupture. Intraplaque hemorrhage (IPH) is a marker of complicated-plaque formation, responsible for many of the clinical manifestations of atherosclerotic disease. Magnetic resonance imaging (MRI) has emerged as a modality to image carotid AP. The in-vivo high-resolution MR imaging of carotid complicated-plaque forms the basis of this thesis. In the first part, Magnetic Resonance Imaging of Intraplaque Hemorrhage (MRIPH), an in-vivo high-spatial-resolution 3-dimensional MRI sequence specifically designed to depict complicated-plaque in the carotid arteries is described. MRIPH was applied, as compared with histologic analysis (gold standard), to demonstrate that T1-hyperintense intraplaque signal represented blood products. Strong agreement was seen between T1-hyperintensity and histologically-identified hemorrhage, with high sensitivity/specificity/positive- and negative-predictive values for T1-hyperintense detection of hemorrhage.
While IPH increases plaque rupture risk, high degrees of calcification promote stability. Calcium can generate T1-hyperintensity in some gradient-echo (GRE) sequences. Therefore, distinction between these two components is crucial. In the second part, T1-hyperintensity in MRIPH was shown to be almost exclusively due to hemorrhage and not calcification by directly comparing in-vivo T1-hyperintensity with calcification in ex-vivo specimens imaged with microCT. T1- hyperintesity showed very good albeit inverse agreement with calcification and excellent agreement with lack of calcification as seen on microCT.
IPH is thought to be the result of rupture/leakage of the vasa vasora. In the third part, we tested the hypothesis that if IPH were due to vasa vasorum rupture/leakage, the majority of the IPH would be associated with the adventitial rather than the luminal surface of the plaque. Deep (closer to vessel wall) and superficial (closer to vessel lumen) regions of complicated plaques were identified. Very good inter-rater agreement was seen for the location of IPH using MRIPH, with IPH being more frequently present in the deeper compared to superficial segments of the plaque.
In summary, an in-vivo MR technique to detect IPH at high spatial-resolution in carotid complicated-plaque was developed; demonstrating T1-hyperintensity in MRIPH is the result of IPH and not calcification. The predilection of IPH for the deeper segments of the plaques suggests that IPH is due to vasa vasorum rupture/leakage.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/26153 |
| Date | 15 February 2011 |
| Creators | Bitar, Richard |
| Contributors | Moody, Alan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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