Diagnostic imaging of carotid artery walls seeks to identify features of the "vulnerable plaque". Vulnerable plaque is defined as an atherosclerotic lesion that poses increased risk of causing thromboembolic events. Histological studies in various vascular beds have established that plaque tissue composition and distribution may strongly influence its clinical course. For example, a thin fibrous cap covering a large lipid-rich necrotic core appears to be a clear marker of vulnerable plaque. The thinning fibrous cap indicates weakened structural integrity and possible future rupture leading to an embolic event. Furthermore, in a landmark study based on coronary autopsy specimens, ruptured fibrous cap, calcium nodules and endothelial erosion were highly associated with sudden cardiac death .
Studies of the carotid arteries have confirmed that similar plaque features lead to brain ischemic symptoms. Specifically, thinned and ruptured fibrous caps are significantly more common in patients with symptomatic carotid arteries . Other features of carotid plaques associated with patient symptoms are ulceration, luminal thrombus in conjunction with ulceration, the presence of large neovessels, and foam cell infiltration into the fibrous cap , , .
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