Performance of Contrast Enhanced Magnetic Resonance Angiography 51 Introduction Magnetic resonance angiography (MRA) has some advantages over computed tomographic angiography (CTA): no harmful ionizing radiation or iodinated contrast agent and no image degradation arising from vascular calcifications and surrounding bony structures. Therefore, MRA might be a preferable diagnostic tool in the detection of intracranial aneurysms in patients presenting with a subarachnoid hemorrhage (SAH). Few direct comparisons between the two modalities have been published. White et al. described the performance of CTA and MRA ten years ago in a meta-analysis.1 The results of their review did not allow direct comparison between CTA and MRA because few studies included patients who underwent both CTA and MRA. In a prospective study White et al2 performed CTA as well as MRA in 142 patients. The diagnostic performance of both modalities did not differ significantly and was not better than in the review performed by the same group. The sensitivity was low, especially for detection of small aneurysms: 57% for CTA and 35% for MRA for aneurysms smaller than 5 mm. It was expected that future improvements in scan technique would lead to better performance, and that the addition of contrast enhanced MRA especially would contribute to this improved performance. All MRA studies in the review as well as their own study used non-contrast-enhanced sequences such as time-of-flight (TOF)-MRA or phase contrast (PC)-MRA. 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.3-5 It might therefore be advantageous in the depiction of intracranial aneurysms. Only a few studies have been performed to evaluate the diagnostic performance of CEMRA in the detection of cerebral aneurysms,3-8 involving only small numbers of patients (4-41 patients) and aneurysms (4-25 aneurysms). The largest series was published by Nael et al7 with 25 aneurysms in 41 patients. In this study CEMRA was compared with CTA for the detection and characterization of cerebral aneurysms, without digital subtraction angiography (DSA) as the reference standard. Therefore, the diagnostic accuracy of the two techniques could not be assessed. The performance of both techniques was excellent in terms of interobserver agreement and of correlation between the two modalities. In the smaller studies of Metens et al4, Suzuki et al8 and Unlu et al5, both CEMRA and DSA were performed. All aneurysms in these three studies, except for one small (2mm) aneurysm,5 were detected by CEMRA. All three groups concluded that CEMRA performed better than TOF-MRA. Specificity could not be defined in these studies because only patients harboring at least one aneurysm were included, so no false positive scores were possible. In view of the sparse data about the performance of CEMRA in the detection of cerebral aneurysms in patients presenting with a SAH, and the lack of data about the compariitive accuracy of CEMRA and CTA, we undertook a prospective study to assess the accuracy of CEMRA in comparison with CTA. We recognize that diagnostic accuracy is not the only factor determining the practical utility of a technique in a demanding clinical situation. Because catheter DSA is an integral part of the coiling procedure, and
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