|ECR 2013 / C-2592|
|Characterisation of Neovascularization in Carotid plaque|
Vulnerable carotid plaques:
Stroke is the third cause of death (1). Unstable carotid artery atherosclerotic plaques cause 25-30% of all strokes (2).
Atherosclerotic plaques tend to progress rapidly. Those with a high tendency to cause thrombotic complications, such as myocardial infarction or stroke, are defined as “vulnerable” plaques/ lesions (3).
As carotid plaques are a major cause of ischemic stroke (Fig. 1). It would be beneficial to identify patients at high risk of ischemic stroke attributable to carotid artery disease. These patients may then benefit from timely preventive therapy. The same test may be used for non-invasive monitoring of the preventive treatment and thus potentially contribute to reversing the course of the disease process (4).
Broadly speaking, the main risk factors related to carotid disease which predispose to ischemic stroke are the degree of stenosis, plaque size and morphology, inflammation, neovascularisation, and downstream effects of atherosclerosis (Fig.2) (5). However, according to recent studies (6), more than 70% of plaque raptures taking place upon luminal stenosis of less than 50%.
Neovessels under the spot light:
Neovascularisation is: the formation of new functional microvascular networks.
How does it progress: In healthy vessels, the vasa vasorum is located in the outer part of the vessel wall, and the intima is supplied by oxygen diffusion from the lumen. As disease develops, the intima thickenss increases, and oxygen diffusion is inhibited. Hence, the vasa vasorum turns into a major source of nutrients for the vessel wall (Fig. 3). The vasa vasorum structure consists of a network of small arteries and veins (7).
Why it is a concern?
Neovessels are alleged to be associated with rapid expansion of atheromatous plaque as a method of entry for lipids, inflammatory cells and red blood cells (Fig. 4). Therefore, neovessels are implicated as a forerunner of plaque vulnerability (8). Furthermore, Moreno et al suggested a contributory role for neovascularisation in the process of plaque rupture (9).
Nevertheless, few imaging techniques can be used to detect and quantify this neovascularisation.
Non-invasive imaging techniques for the neovessels:
Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCMRI):
It provides an assessment of the neovessels in plaques. Kinetic modelling of gadolinium uptake have demonstrated correlation with plaque vascularity in carotid artery (10). It is represented by the result of blood supply vessel surface area and permeability represented by transfer constant (Ktrans value) and the simpler value fractional plasma volume Vp – correlated with microvessel density.
Dynamic Contrast Enhanced Ultrasound (DCUS)
Enhancement of the plaque is well correlated with the histopathological results regarding the area of neovascularisaion. Either subjective (experienced observer) or quantitative analysis implied in preliminary studies. Eventhough almost half of the previous studies used quantitative method to analyse the data, only one research group combined a quantitative method with histology (11). Different doses of contrast media have been used. Standardisation of the technique could be highly useful.
Even MRI proved to be useful tool to detect the Neovascularisation, it has it's pitfalls of being relatively an expensive tool and it is not suitable for many patients for different reasons, such as: claustrophobia, noise, long procedure time, the nature of contrast media which is not compatible with patients with renal failure. Also it won't be suitable for patients with metallic implantations. On the other hand, not many studies tested ultrasound against histology using quantitative analysis. The reproducibility of the studies is higher when it is less subjective.
Hence, the idea of comparing MRI to ultrasound among the same sample of patients in order to get a better idea in which technique is more feasible. Also, making use of a quantitative method to analyse the Ultrasound data and correlate it to histology.
Thematically related posters
ECR 2013 / C-2390
The stenosis of transplant renal artery diagnosed with contrast-enhanced ultrasound (CE-US) - preliminary report
ECR 2013 / C-1751
Quantification of arterial blood flow in patients with bilateral kinking of the internal carotid arteries using phase contrast MRI