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Letters to the Editor |
and
Will Hollingworth, PhD
Department of Radiology, Addenbrooke’s Hospital, Box 219, Hills Road, Cambridge CB2 2QQ, England*, e-mail: jhg21@cam.ac.uk. Institute of Public Health, University of Cambridge, England
Editor:
The interesting article by Dr Randoux and colleagues in the July 2001 issue of Radiology (1), in which gadolinium-enhanced magnetic resonance (MR) angiography was compared with conventional angiography and computed tomographic (CT) angiography, is an important contribution to our assessment of the recently developed MR angiographic technologies. Authors of a number of studies (2–10) have reported the encouraging use of gadolinium-enhanced MR angiography in the assessment of carotid stenosis, with the ultimate aim of reducing some of the risks associated with conventional angiography, as well as cost.
While Dr Randoux and colleagues state that the "statistical power of our work is limited," they go on to state MR angiography or CT angiography "can be used to adequately evaluate carotid stenosis." The Huston et al (3) evaluation of elliptic centric contrast-enhanced MR angiography in 50 patients who underwent conventional angiography took a more realistic and considered approach, which suggests that their technique "appear(s) to be adequate to replace conventional angiography in most patients examined prior to carotid endarterectomy." Although the statement of Dr Randoux and colleagues that sensitivity for MR angiography was very good (93%), the 95% CI (76%, 100%) appears to be large.
Before we can advocate the use of gadolinium-enhanced MR angiographic techniques, of whatever type, to replace conventional carotid angiography, we ideally need to prove that the newer techniques are at least as good as the standard of reference. There may be financial and clinical pressures to replace conventional angiography with a less invasive method of assessing carotid stenosis; however, the radiologic community should strive to ensure that newer techniques are both effective and efficient.
The importance of study design cannot be overemphasized (11). We are currently involved in a study in which we intend to show that gadolinium-enhanced elliptic centric MR angiography is as good as conventional angiography of the carotid bifurcations. To do this, we are examining nearly 200 patients, which should produce a more definitive answer. The disadvantage of our current study is that technologic advances continue relentlessly. Some would argue that such large and expensive studies are indeed futile, as the technology is already a few years out of date when they eventually get published. We would argue that it is vital to validate new technologies, when appropriate, so that clinicians and patients can make informed decisions about optimal imaging strategies.
REFERENCES
Department of Neuroradiology of Professor Marsault, Groupe Hospitalier Pitié-Salpêtrière, Bâtiment Babinski, 47-83 Boulevard de l’Hôpital, 75651 Paris Cedex 13, France. e-mail: bruno.randoux@caramail.com
We appreciate the comments of Dr Gillard and colleagues regarding our article (1), in which we conclude that MR angiography or CT angiography can be used. We agree that MR angiography performs sometimes not as well as digital subtraction angiography (DSA), mainly because of lack of spatial resolution. In these particular cases, we use CT angiography. At our institution, we do not use DSA for diagnostic purposes, because either MR angiography or CT angiography is sufficient. We did not conclude that MR angiography was better than DSA to adequately evaluate carotid stenosis. Because of the risks associated with DSA, we believe that MR angiography can usually be used to respond to the question of vascular surgeons: Is there an indication for surgery?
Investigators in the NASCET study (2) concluded that the risk of stroke could be reduced by performing carotid endarterectomy in symptomatic patients with a stenosis of more than 70%. We used the NASCET criteria because there is clinical effect. We can agree that the 95% CI appears to be large in this study, but we are not sure that there is a clinical interest to distinguish a 75% stenosis from a 90% stenosis. Furthermore, even if the degree of stenosis is important, we believe that plaque morphology is underevaluated. Some study findings have shown that the presence of ulcers was of clinical importance. DSA is not an adequate technique because of lack of plaque visualization. CT angiography, by depicting the atheromatous plaque, thus has an advantage: It is much easier to determine the exact degree of stenosis, and plaque morphology can be evaluated, even if further studies are needed with histologic correlation.
We conclude that in 2001, carotid bifurcation stenosis can be evaluated without the need for DSA. MR angiography is often the examination of choice at many institutions. Nevertheless, we believe that CT angiography is highly accurate and should be performed when there is a discrepancy between the ultrasonographic examination and MR angiography.
REFERENCES
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