Simulation study employing different scenarios 77 Introduction At the present time the gold standard for imaging the cerebral vessels in patients suspected of harboring an intracranial aneurysm is digital subtraction angiography (DSA). The risk of complications associated with cerebral DSA, although low, is not negligible.1-4 Therefore a search is ongoing for an adequate non-invasive alternative for imaging the cerebral vessels and aneurysms originating from these vessels. Alternative techniques presently in use are computed tomographic angiography (CTA) and magnetic resonance angiography (MRA). MRA is a less invasive technique than DSA, but quality of MRA images is also somewhat less. The image quality is however generally adequate for aneurysm detection.5-10 The value of MRA has been established in screening for asymptomatic cerebral aneurysms11 and for assessing aneurysm occlusion after endovascular coiling.12-14 When a patient presents with a subarachnoid hemorrhage (SAH) and MRA fails to reveal a cerebral aneurysm as the cause of bleeding, a DSA study is indicated to confirm the normal findings. First-pass or contrast enhanced magnetic resonance angiography (CEMRA) has shorter acquisition times than flow dependent MRA sequences and does not suffer from signal loss due to turbulent or slow flow or as a result from spin saturation in larger scan volumes which might improve diagnostic accuracy.6,8,9,15-17 The present study deals with the assessment of CEMRA for the detection and characterization of cerebral aneurysms. The diagnostic work up of patients suspected of harboring an intracranial aneurysm comprises more than only detecting the aneurysm. The morphology of the aneurysm must be ascertained in order to determine its suitability for the preferred endovascular treatment, its “coilability”. Criteria determining the feasibility of endovascular coiling are the neck-to-dome ratio of the aneurysm as well as the absolute size of the neck, and the absence of branch vessels at the neck of the aneurysm. Aneurysms which are not suitable for coiling on the basis of these morphological criteria, are referred for surgical clipping if possible. If an aneurysm is classified incorrectly on the basis of the CEMRA findings the consequences may be as follows: x When the aneurysm is mistakenly regarded as being suitable for endovascular coiling this will result in an unsuccessful attempt to coil aneurysm under general anesthesia. x When the aneurysm is mistakenly regarded as being unsuitable for endovascular coiling and the patient is referred for neurosurgical clipping while in fact the aneurysm is suitable for coiling, the patient is denied the benefits of endovascular treatment as documented in the International Subarachnoid Aneurysm Trial (ISAT).18 If CEMRA were to replace completely the more costly and invasive DSA examination, its performance in detection and morphologic assessment of cerebral aneurysms would need to be fully equivalent to that of DSA. As this is presently not the case, strategies will need to be devised in which CEMRA can be employed as initial study, followed if necessary by DSA, with the aim being to reduce as much as
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