Performance of Contrast Enhanced Magnetic Resonance Angiography 59 performance of CEMRA is not significantly different from that of CTA; moreover, it appears to be better than in the published studies using TOF-MRA.1,2 Figure 5. a. Anteroposterior projection of a volume rendered reconstruction of the CTA scan of a patient with a left middle cerebral artery aneurysm. Despite suboptimal image quality due to venous contamination and movement artefacts both observers correctly described the aneurysm. b. Anteroposterior projection of a volume rendered reconstruction of the CEMR scan of the same patient as in Figure 5a. The left middle cerebral artery aneurysm was properly described by both observers. In clinical practice where patients with negative CTA or CEMRA will undergo diagnostic DSA, specificity is of more importance than sensitivity. A false-positive result may ultimately lead to an unnecessary surgical intervention11 or a DSA examination at the start of a coiling procedure under general anesthesia which is then aborted when no aneurysm is found. In our series the specificity for CEMRA is lower than for CTA, although not significantly so. In most hospitals MRI is less easily available than CT. Transporting the patient from the CT scanner, where the diagnosis of SAH is ideally made, to the MRI scanner for aneurysm detection and classification by CEMRA is cumbersome, and patient monitoring is more difficult in the MRI room. Furthermore patient motion is more likely to degrade image quality with MRI than with CT. In our population only six patients were too restless to go into the MRI scanner, though they had already been able to undergo CTA. Contraindications such as implanted pacemakers, intraocular metal fragments and claustrophobia will exclude another group (ten patients in our population). These MRI drawbacks make this modality less popular even though it has the advantage of not employing iodinated contrast media and ionizing radiation.12 The use of gadolinium chelates as a contrast agent for CEMRA involves the risk of inducing nephrogenic systemic fibrosis.13 In the patient population included in our study this is normally not an issue: most SAH patients are relatively young and healthy, and the risk of contrast-induced nephropathy from iodinated contrast media is higher.14 In our population there were no patients with severe renal insufficiency. Additionally, the risk of other adverse reactions is higher with iodinated contrast material than with gadolinium based contrast agents.14
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