Introduction and historical background 17 well as its ability to detail anatomic features and predict whether endovascular treatment is feasible.120,159,160,173,175,179,191-193,199-203 In order to accomplish these feats, the diagnostic tool must permit accurate measurement of the neck width and neck-to-dome ratios, as well as visualization of possible arterial branches originating from the neck of the aneurysm. The latter is important because, for aneurysms with a wide neck or large neck-to-dome ratio, or with branches originating from the neck of the aneurysm, surgical instead of endovascular treatment is preferred in most cases. Some authors report an overestimation of neck-to-dome ratio by CTA141,202 which potentially leads to a choice for surgical treatment where endovascular treatment might have been possible. However, most authors assessing CTA as a diagnostic tool for SAH conclude that, in the majority of cases, CTA is able to fulfill the requirements for optimal treatment planning120,159,179,193,201,203 limiting the need for DSA.160,199 Others still consider DSA the first line imaging modality for patients presenting with SAH.66,68,204 There are on-going heated debates on this issue as exemplified by the following quotes:205-207 “However, in the vast majority of patients with aneurysmal SAH, it (CTA) seems redundant. Perhaps we should, as has been suggested before, “dispense with the CTA altogether and just get on with the appropriate test”68,204 and “When reading the editorial by Kallmes et al, one cannot help conclude that their protests are the obligatory last spasms of a dying, outclassed, antiquated way of practice that is the “diagnostic” catheter angiogram.”205 We suggest that an appropriate diagnostic strategy following the detection of an aneurysm through CTA could be as follows: • If CTA clearly depicts the neck of the aneurysm, and side branches can be identified properly, treatment planning can be done using CTA alone. • If doubt exists about these characteristics an additional (preferably rotational) DSA examination should be performed. It is important to note that, in these recommendations, cost-effectiveness of the different diagnostic strategies was not taken into consideration. Detection and evaluation of intracranial aneurysms: MRA A third alternative tool in the search for aneurysms in patients presenting with a SAH is magnetic resonance angiography (MRA). After the detection of ‘magnetic resonance’ by Bloch and Purcell in the 1940’s,208,209 Paul Lauterbur was the first to write a paper about imaging using this technique in 1973210 which he called zeugmatography. Lauterbur realized what potential the new technique had for medical imaging and speculated that: “a possible application of considerable interest at this time would be to the in vivo study of malignant tumors, which have been shown to give proton nuclear magnetic resonance signals with much longer water spin-lattice relaxation times than those in corresponding normal tissues.” The possibility to discriminate between malignant tumors and normal tissue using spin echo nuclear magnetic resonance measurements had already been described by Damadian in 1971.211 The first clinical applications of magnetic resonance imaging (MRI) were described by Mansfield and Maudsley in 1977212 and the development of magnetic resonance angiography (MRA) began in the early to middle 1980s.213,214
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