Performance of Contrast Enhanced Magnetic Resonance Angiography 65 Introduction If a non-invasive imaging technique is to be employed in the work up of patients presenting with a subarachnoid hemorrhage (SAH), accurate detection of a possible intracranial aneurysm is of primary importance. In addition however, the technique in question should permit an assessment of the possibility of endovascular treatment: its ‘coilability’.1,2 In Chapter 2 the accuracy of contrast enhanced MRA (CEMRA) in detecting an aneurysm in patients presenting with a SAH is described and compared to that of CT angiography (CTA).3 In this chapter the capability of CEMRA and CTA to predict the coilability of an intracranial aneurysm and the respective accuracies of the two modalities in aneurysm size measurement are evaluated, using DSA as standard of reference. The capability of selecting the appropriate mode of treatment for intracranial aneurysms using CTA, has been studied and described in several papers.4-12 Most authors conclude that in the majority of cases CTA is able to guide treatment planning, thus limiting the need for additional digital subtraction angiography (DSA).4,5,11 Only few studies have appeared describing the use of MRA to assess the feasibility of endovascular treatment,13-16 and no direct comparison with CTA was made in these studies. The conclusions of these studies varied from ‘MRA appears to be an effective treatment planning tool for most patients with SAH’13 to ‘MRA cannot replace DSA in treatment planning’.16 Important criteria determining the feasibility of endovascular coiling are the neck-to-dome ratio of the aneurysm and the absolute size of the neck and of the aneurysm. In vivo studies have been performed to assess the reliability of aneurysm volume measurement with CTA and MRA17,18 reporting good correlation with DSA. Some authors report overestimation of neck-to-dome ratio by CTA.19,20 The advantages of MRA over CTA have been pointed out in Chapter 2: there is no use of harmful ionizing radiation or iodinated contrast agents, and bony structures or vessel calcifications do not hinder evaluation of the vascular structures. Signal loss due to turbulent or slow flow, which may degrade the image in flow dependent MRA sequences, do not occur in CEMRA.16,21,22 There are logistical limitations involved in performing a MRA study in the acute setting of a patient with a SAH. Frequently there is no immediate availability of an MRI system, and there is the necessity of transporting the patient from the CT scanner, used in diagnosing SAH, to the MRI system. Furthermore there may be problems related to patient unrest and poor patient monitoring inside the bore of the magnet. These drawbacks make MRA a less attractive alternative. Therefore CEMRA could be a preferable diagnostic tool in the patient work up only if it were to perform better than CTA in detecting intracranial aneurysms or predicting the feasibility of endovascular treatment.
proefschrit Van Zwam inhoud met kaft en stellingen.indd
To see the actual publication please follow the link above