Patients with a moderate to severe carotid atherosclerotic plaque are at risk for stroke and this risk increases with increasing degree of stenosis. It has been shown that carotid endarterectomy in symptomatic patients with a carotid artery stenosis of 70-99% is highly beneficial. However, the beneficial effect of surgery in patients with symptomatic 30-69% stenosis is not clear yet.A clear beneficial effect of surgery in the 30-69% stenosis group might be found in a sub-group of patients whom are at greater risk for stroke. Definition of this sub-group might be achieved by plaque characterization, since rupture of a vulnerable plaque is the main cause of stroke due to carotid artery stenosis.This study will include patients with a 30-69% carotid artery stenosis, and assess plaque composition by MRI, the degree of plaque inflammation by FDG-PET, and the amount of microembolization by transcranial Doppler ultrasound. The main purpose of this study is to assess whether one or a combination of each of these imaging methods can predict the occurrence of a (recurrent) ischemic stroke.