الفهرس 
Anatomy of the Carotid and Vertebral ArteriesOnly 14 pages are availabe for public view
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Abstract
Cerebrovascular Stroke is one of the leading causes of morbidity and mortality worldwide. Carotid arterial occlusive disease is responsible for up to 25% of these strokes. 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.
The accepted gold standard for evaluation of carotid artery stenosis is catheter angiography; however, this technique is expensive and invasive and has substantial risks.
Colour Doppler sonography is a safe, relatively inexpensive and noninvasive method for detection of stenosis in the carotid artery. However, large variability exists in the performance of Doppler sonography to reliably assess haemodynamicaly significant carotid stenosis.
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 stenosis. For the preoperative evaluation, diseases that require surgery (70%–99% stenosis) must be differentiated from diseases that do not require surgery (stenosis less than 70%). With current noninvasive imaging modalities, it has been proved that 3D CT angiography has a high discrimination rate between severe stenosis and occlusion.
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. 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 radiation.
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 views, 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.
Interpretation of the complex vascular system necessitates viewing of several contiguous sections or views, and usually the interpretation of CT angiograms is performed interactively on a workstation. 3D reconstructions such as maximum intensity projection (MIP) and volume rendering (VR) are able to display complex arterial anatomy and the findings in a single view.
MIP images are created using a computer algorithm that evaluates each voxel and selects the voxel with the maximum intensity as the value of the corresponding display pixel. The resulting image is displayed as a two-dimensional representation. The major limitation of the MIP algorithm is vessel calcification.
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 with oblique MPR images had excellent detection of stenosis, and the sensitivity and specificity reached 100% for detecting stenosis of 70% or more.
CT angiography also demonstrates atherosclerotic changes inside the arterial wall with some morphologic characteristics of the plaque. Ulcerative plaques in carotid arteries may be the source of thromboembolism into the cerebral circulation. There was an agreement between the modalities for the detection of ulceration in the present study.
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.
Multislice CTA with the ability of 3D reconstruction imaging plays an important diagnostic role in assessment of extracranial carotid artery stenosis. CTA stands in direct competition with color duplex ultrasound and MR angiography for accurate grading and post therapeutic evaluation as a minimally invasive alternative to conventional angiography.