الفهرس 
ANATOMY OF CAROTID ARTERIAL SYSTEMOnly 14 pages are availabe for public view
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Abstract
Stroke is a dramatic medical problem. It is one of the leading causes of morbidity and mortality worldwide. When considered separately from other cardiovascular diseases, stroke is the third among all causes of death, behind diseases of the heart and cancer. Carotid artery atherosclerotic is an important etiological factor for ischemic stroke . Findings of large population-based studies indicate the prevalence of carotid artery stenosis is approximately 0.5% in the 6th decade and increases to 10% in persons over 80 years of age. The vast majority of cases are asymptomatic. The main purpose to diagnose carotid artery disease is prevention of stroke in a high-risk population. An accurate noninvasive imaging study is necessary to determine the indications for carotid endarterectomy or stenting in both symptomatic and asymptomatic patients with significant internal carotid artery stenoses.
Actually clinical decision making regarding intervention for carotid artery stenosis depends upon the grade (percentage) of stenosis . The results of two large randomized trials-the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST) have shown carotid artery endarterectomy to yield a considerable advantage in patients with 70–99% stenosis and a small benefit in symptomatic patients with 50–69% stenosis.
In these studies, digital substraction angiography (DSA) was the gold standard for the evaluationof carotid stenosis but also associated with an increased risk of thromboembolic events and marked financial cost.
Recent works, however, put in evidence the need of assessing additional plaque morphologic parameters in order to better define the most correct therapeutic treatment .In fact, assessment of luminal stenosis alone is limited in the prediction of the clinical outcome and the natural history of the disease. The “vulnerable” carotid plaque identifies an atherosclerotic plaque which is characterized by an higher tendency to rupture, potentially resulting in embolization or thrombosis.
Consequently, numerous noninvasive imaging techniques are used in the evaluation of carotid artery degree of stenosis and in depicting the internal constituents of carotid plaque including: magnetic resonance imaging (MRI), ultrasound sonography (US), and multidetector row computed tomography angiography (MDCTA).
Colour Doppler sonography is a safe, relatively inexpensive and noninvasive method for detection of stenosis in the carotid artery without the risk related to ionizing radiation and contrast material nephrotoxicity. However, this technique suffers from inter-observer and intraobserver variability in the measurements, determined by several parameters (e.g. sonographer experience and type of sonographic scanner).
The evolution of multislice CT has allowed the development and advancement of CT angiography (CTA). New multislice CT technology provides several advantages for carotid imaging. CT angiography is a reliable and fast technique to evaluate the degree of ICA stenosis. Also,it has been proved that 3D CT angiography correlates well
with catheter angiography and has a high discrimination rate between severe stenoses and occlusions.
CT angiography has some substantial benefits, including its accuracy and lack of invasiveness, compared with DSA. It is also an inexpensive and easily accessible technique. Limiting factors are the use of potentially nephrotoxic contrast media and an ionizing technique.
Multislice CT angiography permits larger anatomic coverage, including both the epi-aortic and entire carotid circulation with the branches of the circle of Willis. Thus, symptomatic carotid disease could be identified immediately, and treatment decisions could proceed more rapidly; alternatively, elimination of the carotid arteries as a source of emboli could direct the workup toward other sources, including the heart and the intracranial vasculature.
CT angiography provides several methods to display vascular structures. Axial source images and MPRs are the most informative images, containing all the information of the entire imaged volume, such as enhanced vascular structures, plaques in the arterial wall with or without mural calcifications, and extra-vascular tissues. When using interactive interpretation of axial sections, MPRs, and the 3D view, neither mural calcification nor enhanced jugular veins hamper the visualization of the carotid artery, and the carotid artery anatomy in relation to facial bones can also be displayed.
In recent years VR has become the single most useful and versatile 3D imaging technique. Unlike a MIP image that takes only the highest density value for a given ray, with VR no information is lost or discarded, and every voxel contributes to the final image. The resulting images therefore contain more information and are potentially much more clinically useful. This allows volume rendered images to display multiple tissues and show their relationships to one another.
The powerful computers of the workstation today allow easy generation of the 3D views; thus, for example, VR views are quickly available for the overview of the vascular anatomy and for demonstration of findings to the referring physician.
However, the radiologist must be aware of the technical principles underlying those 3D reconstruction methods to avoid pitfalls in the evaluation of vascular lesions. Interpretation of CT angiography should always include analysis of the entire imaged volume interactively at the workstation by using axial images, MPRs, or both.
In this study, Carotid CT angiography shows good correlation with CD-US in terms of categories of stenosis, and types of atheromatous plaques. The accuracy of CT angiography for quantification of carotid artery stenosis and characterization of atheromatous plaque type was high in our study (being 94.4% and 91.1% respectively), which is in agreement with that of previous studies.
However, CT angiography has the potential to be used as a screening method for symptomatic patients with cerebrovascular disorders. Also, It has been found that the carotid CT angiography is a non-invasive and valuable tool for detecting stenosis in patients with high risk of developing stroke. The most common imaging technique for the primary diagnostics of hemispheric infarcts is CT of the brain. CT angiography could be easily performed in the same session for these patients at considerably lower cost compared with MR angiography, and without transfer of the patient to another imaging unit.
In conclusion, though DSA remains the gold standard in quantification of carotid artery stenosis, its use is declining due to the complications it presents. 3D CT angiography with a high-performance workstation provides detailed images with satisfactory information by providing greater accuracy both in the assessment of the degree of stenoses and in the characterization of plaque contents.