## 3 Results
plaque angiogenesis is critical in the progression of atherosclerotic carotid plaque [22]. Similar to [PERSON] et al. [33], we found a higher microvessel density in the carotid unstable plaques in association with macrophage infiltration compared with stable plaques, confirming that intraplaque neovascularization is also a marker for plaque instability. According to other researchers [34], the symptomatic carotid disease has been associated with intraplaque hemorrhage and plaque instability. These features of the lesion can be influenced by the fragility of neovessels within the plaque [22]. Neovascularization developed from adventitial vasa vasorum as an adaptive response to hypoxia may cause subsequent intraplaque hemorrhage and plaque rupture [33]. Intraplaque hemorrhage is considered one of the identifying features of vulnerable plaque [34]. The true role of plaque calcification remains a matter of debate [6; 35]. According to [PERSON] et al. [23], micro-calcifications located within the fibrous cap are critical for plaque destabilization, whereas intraplaque macro-calcification has been connected with stronger stability of atherosclerotic plaques. A digital quantitative method confirmed the features of unstable plaques obtained by semi-quantitative methods in specimens obtained by carotid endarterectomy, and was used to more precisely measured the amount of fibrous tissue, lipid core size, cap thickness, inflammatory cell infiltration, and intraplaque hemorrhage size as the major determining factors of plaque [36]. In addition, the digital method also measured CD68 and CD3 cells in the fibrous cap and plaque tissue separately, allowing for a more detailed characterization of each plaque. The quantitative method was used to calculate a vulnerability index by histologically analyzing the carotid plaque: the smooth muscle cells (alpha-actin), lipids (Oil Red O), macrophages (CD68), hemorrhage (glycophorin A), and collagens [37]. The risk of future postoperative cardiovascular events was two times higher among patients having a high vulnerability index score than those having a lower score. The central role of inflammation and proteases in plaque instability was highlighted by gene expression analyses in endarterectomies from patients with carotid stenosis. These studies identified the genes linked to plaque instability and also plaque phenotypes (i.e., calcification or lipid-rich necrotic core content) [38]. [PERSON] et al. proposed a panel of 30 genes, mostly transcription factors, to differentiate between plaques in symptomatic versus asymptomatic patients, including gene networks associated with atherosclerosis mapped to hypoxia, chemokines, calcification, the actin cytoskeleton, and the extracellular matrix [38]. In addition, [PERSON] et al. performed an integrated analysis of symptomatic carotid stenosis patients at increased stroke risk with transcriptomic and clinical data and demonstrated that the state of plaque instability was more clearly related to enriched pathways coupled to neovascularization, ongoing coagulation, angiogenesis, iron homeostasis,endothelial cell migration, and wound healing, which are all linked to neovessel formation and IPH [39]. There was moderate consistency between the assessment of plaque vulnerability by hematoxylin-eosin (HE) histopathological examination and by 2D-ultrasound (\(p>0.05\)) [40]. However, there was a strong consistency between the assessment of plaque vulnerability by contrast-enhanced ultrasonography (CEUS) and histopathological HE (\(p<0.01\)) [41] in patients who underwent carotid endarterectomy. The area under the curve (AUC) of the carotid plaque detected using CEUS was positively correlated with histologically quantitative parameters: microvessel density (\(p<0.001\)), collagen type I/III ratio (\(p<0.001\)), and MMP-9 and matrix metalloproteinase (MMP)-9 expression (\(p<0.001\)) [42].