Introduction and historical background 19 sensitivity was slightly lower than CTA: 87% (95% CI: 84 – 90%), but the difference in MRA sensitivity between large and small aneurysms was even greater than CTA: 94% (95% CI: 90 – 97%) for aneurysms larger than 3mm versus 38% (95% CI: 25 – 53%) for aneurysms smaller than 3mm. There were no contrast enhanced MRA studies included in this meta-analysis, and the authors expected improved outcomes with these newer techniques. From 1998 to 2004 the department of Radiology of Maastricht University Medical Centre (MUMC) performed several studies with CEMRA in other areas of vascular imaging such as imaging of peripheral256-260 and renal arteries.261,262 In continuation of this line of research a study was designed to assess the performance of CEMRA in the detection of cerebral aneurysms in patients with a SAH: Magnetic resonance Angiography with Contrast in Cerebral Aneurysms (MACCA). This study is described in Chapter 2: Performance of Contrast Enhanced Magnetic Resonance Angiography in patients presenting with Subarachnoid Hemorrhage. Part 1: detection of aneurysms To define the true value of MRA in the diagnosis and treatment of SAH it is important not only to determine its diagnostic sensitivity but also to evaluate its performance in assessing the feasibility of endovascular treatment. This has been done in a few studies, but the lack of a good standard of reference poses a problem in assessments of this kind. Feasibility of endovascular treatment, or “coilability”, of an aneurysm, depends on many factors -of which a few have been mentioned above- but assessment of coilability appears to be very subjective. In most studies evaluating the efficiency of non- invasive techniques in the assessment of coilability of an aneurysm, the neck-to-dome ratio was measured and sometimes compared to measurements made using DSA, and shape or lobulation of the aneurysm as well as parent and branch vessels were described and evaluated.263-266 In these studies TOF MRA was used. The main limitation of TOF MRA in the assessment of aneurysm morphology lies in the fact that high intravascular signal represents flow rather than the true boundaries of the aneurysm. In TOF MRA, slow flow within the aneurysm may not be registered, and thus an incomplete and incorrect image of aneurysm morphology may be presented.228 Unlu et al. evaluated the performance of CEMRA in the assessment of aneurysm morphology with a 1 Tesla MRI scanner, and concluded that: ‘the mean grade of aneurysm depiction, depending on morphology of the aneurysm, the shape of the neck and relationship of the aneurysm with parent and branch vessels, was significantly greater with CEMRA than with TOF MRA’. However, these same authors also concluded that: ‘CEMRA cannot yet safely replace DSA in the diagnostic work-up of patients with acute SAH’.267 Neal et al, who used CEMRA in a 3 Tesla system, concluded that CEMRA ‘is reliable for evaluation and characterization of intracranial aneurysms, and that the results are comparable with those of MDCT’.268 In comparison with TOF MRA they found that: ‘TOF and CEMRA perform comparably at 3T for evaluation of intracranial aneurysms. CEMRA can generate sub-millimeter voxels without the sensitivity to saturation or flow effects characteristic of TOF techniques’.269 Their study population was too small to draw strong conclusions however, and Neal et al. stressed the need for larger studies. Two studies evaluated MRA as the only diagnostic modality before surgical treatment.270,271 In both studies a considerable number of patients still required additional DSA imaging (30 and 35.1% respectively), because MRA was inconclusive or no aneurysm was found. Despite
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