الفهرس 
Anatomy of the cerebral arteriesOnly 14 pages are availabe for public view
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Abstract
The leading cause of nontraumatic subarachnoid hemorrhage is rupture of an intracranial aneurysm, which accounts for about 80 percent of cases and has a high rate of death and complications, and prompt detection and evaluation of the aneurysm is critical for determining the appropriate endovascular or neurosurgical intervention.
The current accepted gold standard imaging modality for the evaluation of suspected aneurysms is digital subtraction angiography; however, DSA is an invasive study, time consuming, relatively expensive, with a small but significant 4% risk of complications and 0.07% to 1% reported risk of persistent neurological deficit.
Unlike DSA, MRA has the advantage of high sensitivity to the flow phenomena, therefore cerebral vessels can be displayed without contrast medium administration. However, although MR angiography (MRA) has given very good results in detecting aneurysms in acute SAH , it is often impractical in severely affected patients, due to long examination time, low spatial resolution compared to DSA, high cost, sensitivity to motion artifacts, difficulties in demonstrating vessels with low flow conditions, not providing good delineation of calcium and bony landmarks and is not optimal for assessing post aneurysm clipping status.
Over the last decade, CT angiography has increasingly been used for the early diagnosis and detection of ruptured intracranial aneurysms, and most recently for the CTA provides a much desired noninvasive method of intracranial angiography that allows for multiple techniques of 2D and 3D viewing, including multi-planar reformation (MPR), maximum intensity projection (MIP), shaded surface display (SSD), and direct volume rendering (dVR).The recent introduction of multi-detector row CT has allowed great advances in CTA imaging.
Compared with single-section CT scanners, multi-slice CT scanners offer faster speed, longer distance, and thinner slice thickness as well as volumetric acquisition with considerable improvement in quality and spatial resolution. MSCT systems have evolved from four- to 16- and now 64- channel detector row scanners. With the increase in the number of detectors further increasing the quality of CTA images. Advances in MSCT scanning have significantly improved the ability of CTA to identify and characterize intracranial aneurysms, as compared with DSA, possibly allowing CTA to replace DSA as the preferred method for imaging aneurysms. Moreover, it determine the bleeding etiology in patients with SAH in most cases and allows for precise depiction of aneurysm morphology and site that is mandatory to choose the appropriate treatment.
The location of blood within the subarachnoid space correlates directly with the location of the aneurysm in 70% of cases.
However, there are several pitfalls of MDCT angiography. It is often difficult or even impossible to differentiate the infundibular dilatation of the origin of an artery from an aneurysm, which can lead to false-positive results. the situation can be clarified by lowering the thresholds on the 3D images or by careful inspection of the source images. Aneurysms involving the skull base often do not show very well on 3D images. Analysis is more easily performed by using the section images. Patients with clipped aneurysms represent a specific problem. Beam hardening artifacts produced by the aneurysm clips preclude a clear depiction of nearby intracranial arteries. It is mandatory to carefully inspect the source images prior to 3D visualization to check for the occurrence of artifacts around the clip.