Performance of Contrast Enhanced Magnetic Resonance Angiography 53 Patients All consecutive adult patients presenting with the diagnosis of a non-traumatic SAH were eligible to enter the study. The diagnosis SAH was established by CT or lumbar puncture. Exclusion criteria were as follows: patients in whom there was a contraindication for MRI or in whom no further treatment was considered. A poor clinical condition was no contraindication for inclusion, but if no reasonable chance of survival was expected by the treating physician, then no further diagnostic or treatment procedures would be undertaken and the patient would not be included in the study. Techniques CTA: CTA was performed on a two-slice (Elscint Dual; Elscint, Haifa, Israel) or on a four-slice multidetector- row spiral CT scanner (Toshiba Aquilion; Toshiba, Tokyo, Japan). Scan parameters for the two-slice scanner were: 120 kVp, 250 mAs, collimation width 1,3 mm, pitch 0,7; FOV 250 mm, matrix 340;2 and for the four-slice scanner: 120 kV, 200 mAs, collimation width 0,9 mm, pitch 0,67; FOV 230mm, matrix 512.2 Reconstruction on both scanners to 0,5 mm slices. Contrast: iobitridol 350 mg/ml (Xenetix®, Guerbet, Villepinte, France), IV at 4ml/s, total volume 125 ml, flushed with 40 ml NaCl 0,9% at 4 ml/s. For the Elscint scanner a test contrast bolus of 20 ml was injected to determine the optimal interval between the start of contrast injection and the start of the scan. For the Toshiba scanner a detection slice through the internal carotid arteries was made; scanning began upon arrival of contrast in this slice. Scan direction in both scanners was from caudal to cranial. In most cases a semi-automatic bone subtraction method, Matched Mask Bone Elimination (MMBE), was used. In this method a low dose-mask is acquired of the bony skull, after which the bone-containing voxels are extracted from the post-contrast images, using a computer algorithm that compensates for movements between the scans.9,10 In cases where the patient was too restless to undergo a mask CT scan before the contrast scan or in cases where the contrast scan could not be matched with the mask due to excessive movement between the scans, the contrast scan was evaluated using manual segmentation to remove the bony structures. MRA: MRA was performed on a 1.5 Tesla Philips scanner using a dedicated head coil (Intera; Philips, Best, The Netherlands). The scan protocol included an ultra-short first-pass CEMRA with concentric k-space filling. The scan parameters were: parallel imaging (SENSE, factor 2), TR 5.4 / TE 1.68 ms, flip angle 35 deg, FOV 256 mm (rectangular FOV 65%), matrix 512, slice thickness 0.4 mm, coronal orientation (parallel to basilar artery), one stack, 120 slices. Voxel size 0.5x0.8x0.4mm. Contrast: 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. DSA: All patients underwent conventional catheter DSA (Integris; Philips Medical Systems, Best, the Netherlands). All four feeding arteries to the brain were catheterized and imaged, except for two patients in whom, due to patient unrest, only the vessel which contained the suspected aneurysm was
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