Importance of Fibrous Cap Detection

The development of alipid core marks the development of an intimal xanthomata or fibrous streak into an atherosclerotic plaque. A thin layer of smooth muscle cells form a covering called the fibrous cap (FC) over the lipid core and separate it from the lumen [93]. Rupture of the FC in advanced lesions leads to thrombosis or intraplaque hemorrhage. Inflammatory destabilization of the cap and subsequent thinning are prior events [94]. Thin FCs have been shown to be associated with symptomatic carotid vascular disease [95]. Studies of endarterectomy or postmortem histology identify such association retrospectively but methods of in vivo observation of FC status would enable prospective studies and lead to a better understanding of the pathogenesis. High-resolution MR imaging has shown promise in this regard. T2 [96], 3D TOF [7, 97, 98], and gadolinium-enhanced MR [99] have been used for FC imaging. Examination of multicontrast MRI with black blood (BB) sequences (T1, T2, PD) alongside 3D TOF has been shown to identify three different cap states: thick, thin, and ruptured [97]. A thick FC is considered to be stable while thin and ruptured caps are indicative of vulnerability. The presence of ruptured caps in MRI is highly associated with recent TIA [7]. MRI has shown a high sensitivity and specificity in identifying the three classes of FCs [98].

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