54 Chapter 2 catheterized. A 4 or 5F catheter system was used for diagnostic DSA and a 6F system in cases of anticipated immediate endovascular treatment. Automatic contrast injections were performed by power injector (Medrad Inc., Warrendale PA, USA), of 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 vertebrobasilar arteries in antero-posterior and lateral projections. Additional angiographic projections were obtained, if necessary, of the vessels harboring an aneurysm, for better visualization of the aneurysm, its neck and its surrounding arteries. Image interpretation and statistical analysis The CTA and MRA studies were retrospectively evaluated by two independent observers on a dedicated workstation (Vitrea; Vital Images, Minnetonka, Minnesota, USA). Observers were able to use source images and interactively view volume rendered or maximum intensity projection (MIP) reconstructions. Observers evaluated both modalities in random order, with an interval of at least 12 months between each modality. The DSA images were analyzed by two independent observers; discordant results were settled by a third observer. Scoring criteria included: quality of images, presence of aneurysm, size of aneurysm and diagnostic confidence. Quality of images and confidence in scoring were rated on a three point scale: ‘poor’, ‘moderate’ and ‘good’. Size was given in millimeters in two directions. Sensitivity and specificity for the detection of aneurysms were calculated and compared with McNemar’s test. ROC curves for the two modalities and two observers were calculated and the areas under the curve were compared. For ROC curve calculations the confidence scoring was transferred to a negative value if no aneurysm was found. The resultant values were used for cut-off points. Cohen’s Kappa was calculated for interobserver agreement. Results During an approximate three-year period, a total of 189 patients entered our hospital with a SAH diagnosis. Of these 189 patients 114 (60.3%) could not be included in the study for reasons set out in Table 1. Table 1. Reason for exclusion N - Not enough time between CTA and treatment to perform MRA 57 - Declined additional MRA 22 - Condition too poor to plan further treatment 11 - Contra-indication for MRI 10 - Patient distress, MRA not possible 6 - Died before MRA 4 - No informed consent before treatment (no MRA made) 2 - Died before DSA and treatment, after MRA 1 - Transferred to other hospital for treatment 1 Total excluded 114
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