Introduction

In large randomized trials carotid endarterectomy was shown to be beneficial in symptomatic patients (transient ischemic attack [TIA] or minor stroke in the past 6 months) with a severe stenosis (70–99%) of the internal carotid artery (ICA) (Rothwell et al., 2003). Subgroups of patients with a symptomatic stenosis of 50–69% also benefit from carotid endarterectomy. Recently, even for asymptomatic patients, a small effect of carotid endarterectomy was reported (Halliday et al., 2004). The discussion whether this effect was sufficiently large to advise surgery to (subgroups of) asymptomatic patients is still ongoing (Barnett, 2004). A more recent development is treatment of the carotid artery stenosis with endovascular stenting (Cambria, 2004). Randomized trials are still ongoing to assess the efficacy of this treatment. In the trials with symptomatic patients, an increasing degree of stenosis yielded increasing benefit from surgery. Therefore, precise estimation of the degree of stenosis is crucial for decisions on interventions for carotid artery atherosclerotic disease.

In the trials the degree of stenosis was assessed with intraarterial digital subtraction angiography (DSA), which consequently has become the standard of reference in the selection of patients for carotid endarterectomy. However, DSA has a nonnegligible morbidity and mortality, which decreases the potential overall benefit of endarterectomy (Hankey et al., 1990; Willinsky et al., 2003).