60 Chapter 2 Study limitations: Only 39.7% of all eligible patients presenting during the study period were finally included, mainly due to logistical problems (lack of time for the informed consent procedure and performance of the additional CEMRA study). The patient characteristics and the prevalence of aneurysms, however, did not differ significantly between the total group of 189 presenting patients and the 75 included patients. When patient inclusion for this study commenced it was not yet common practice to employ 3D rotational DSA. Therefore it was decided to use conventional 2D DSA as the standard of reference in all patients. In our practice, all patients with non-perimesencephalic and non-traumatic SAH, in whom the DSA study does not show an aneurysm, are studied by a second or even a third DSA. In the study population, these repeat DSA studies were performed with the knowledge of the CTA and CEMRA findings but no additional aneurysms were found with these repeat DSA studies (except for the one case described above where the thrombosed aneurysm was revealed on a second DSA some days later). Although this is not a guarantee that no additional aneurysms would be found if 3D DSA was used, this would not lead to difference in performance between CTA and CEMRA. 1.5T MRI scanners are still the systems mostly used. The use of 3T scanners has led to better results in the follow-up of coiled aneurysms,15,16 but this improvement has not yet been confirmed for the detection of aneurysms in patients presenting with a SAH. The evolution in CT technique, on the other hand, from the two- and four-detector-row scanners used in our study to 16-, 64- and even 320-detector-row scanners, has definitely led to improved accuracy in the detection of intracranial aneurysms.17-20 It is therefore likely that at the present time CTA with state-of- the-art CT-scanners performs significantly better than MRA in the detection of intracranial aneurysms. Conclusion Using the techniques available at the time of the study, our results indicate that CEMRA does not appear to provide superior diagnostic performance compared to CTA for the detection of cerebral aneurysm in this patient population. Improvements in CTA technique make it unlikely that with present state of the art equipment CEMRA will gain preference over CTA. References 1 White, P. M., Wardlaw, J. M. & Easton, V. Can noninvasive imaging accurately depict intracranial aneurysms? A systematic review. Radiology 217, 361-370, (2000). 2 White, P. M., Teasdale, E. M., Wardlaw, J. M. & Easton, V. Intracranial aneurysms: CT angiography and MR angiography for detection prospective blinded comparison in a large patient cohort. Radiology 219, 739-749, (2001). 3 Jager, H. R. et al. Contrast-enhanced MR angiography of intracranial giant aneurysms. AJNR Am J Neuroradiol 21, 1900-1907, (2000). 4 Metens, T. et al. Intracranial aneurysms: detection with gadolinium-enhanced dynamic three-dimensional MR angiography-initial results. Radiology 216, 39-46, (2000).
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