Simulation study employing different scenarios 79 aneurysm, which was considered as a true aneurysm in the present study and therefore presented to the observers for assessment of its coilability. In another patient a small right internal carotid artery aneurysm, additional to a larger ruptured left ophthalmic artery aneurysm, was not presented to the observers in this study because no treatment was considered for this aneurysm. Techniques MRA: MRA was performed on a 1.5 Tesla system using a dedicated head coil (Intera; Philips Medical Systems, Best, the Netherlands). The scan protocol included an ultra-short first-pass CEMRA sequence with concentric k-space filling. Scan parameters were: parallel imaging (SENSE), TR 5.4 / TE 1.68 ms, flip angle 35 deg, FOV 256 mm (rectangular FOV 65%), matrix 512,2 slice thickness 0.4 mm, coronal orientation (parallel to basilar artery), one stack. The contrast medium employed was: gadopentetate dimeglumine (Magnevist®, Bayer Schering Pharma, Leverkusen, Germany) 35 ml IV, 3 ml/s (2 ml for a timing sequence and 33 ml for the CE-MRA sequence), flushed with 25 ml NaCl 0,9% at 3ml/s. The MRA studies were post-processed and evaluated by the observers using a dedicated workstation (Vitrea; Vital Images, Minnetonka, Minnesota, USA). DSA: All four feeding arteries to the brain were catheterized and imaged in our angiography suite (Integris; Philips Medical Systems, Best, the Netherlands), except for two patients in whom, due to patient unrest, only the vessel which harbored the suspected aneurysm could be catheterized. A 4 or 5F catheter system was used for diagnostic DSA and a 6F system in cases where immediate endovascular treatment was anticipated. Contrast injections were performed by power injector (Medrad Inc., Warrendale PA, USA), delivering 9 ml iobitridol 350 mg/ml (Xenetix®, Guerbet, Villepinte, France) at 5 ml/s for the carotid arteries and 8 ml at 4 ml/s for the vertebral arteries. Internal carotid arteries were imaged in antero-posterior, lateral and oblique projections and the vertebral arteries in antero-posterior and lateral projections. Additional angiographic projections were obtained if necessary, of the vessels that harbored an aneurysm, for better visualization of the aneurysm, its neck and the surrounding arteries. Image interpretation and statistical analysis The CEMRA data were post-processed and the images jointly evaluated on the workstation by the two observers. Scoring criteria were: quality of images, size of the aneurysm, feasibility of endovascular treatment. Quality of images was rated on a three point scale: ‘poor’, ‘moderate’ and ‘good’. Size of the aneurysm was rated on a four point scale: small (<5mm), medium (5-15mm), large (15 – 25mm) and giant (>25mm). Feasibility of endovascular treatment was rated on a two point scale (yes/no) by the observers. Sensitivity and specificity for prediction of coilability were calculated on a per aneurysm basis. For cost calculation the costs of MRA and DSA are derived from the Dutch hospital cost reimbursement system.20 Because controversy exists about the difference in costs of coiling and clipping,21 the cost effect of an incorrect decision with regard to coiling or clipping is not taken into account.
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