The purpose of this study is to determine the frequency, characteristics, and consequences of vulnerable carotid artery plaques ipsilateral to an acute ischemic stroke or TIA in the territory of the internal carotid artery.

Even with extensive diagnostic workup the underlying etiology remains unidentified in about 25% of patients with acute ischemic stroke (AIS) or transient ischemic attack (TIA). Non-invasive high-resolution magnetic resonance imaging (HR-MRI) of the carotid artery allows detecting vulnerable plaques (VP) and quantifying single plaque components. The hypotheses behind this study are that i) a substantial proportion of cases of AIS and TIA within the anterior circulation and no identified cause (cryptogenic AIS or TIA) are caused by VP in the carotid artery; ii) that these patients are at a high risk of developing a recurrent stroke, TIA, or clinically silent lesions detectable by brain MRI; and iii) that VP in the carotid artery are associated with specific infarct patterns as detected by diffusion-weighted MR imaging. Finally, the investigators will search for biomarkers associated with vulnerable carotid artery plaques. Motivating this study are the following considerations: i) data on the frequency and characteristics of VP in patients with cryptogenic AIS or TIA will provide valuable insights into stroke mechanisms; ii) depending on the results this study may have implications for diagnostic decision making and provide the basis for the planning of targeted interventional studies.

Inclusion Criteria:

• Age > 49 years old
• Acute ischemic stroke or transient ischemic attack (TIA)
• Neurological symptoms compatible with a stroke or TIA in the anterior circulation (territory of the internal carotid artery)
• Onset of symptoms within the last 7 days
• 1 or more acute ischemic lesion(s) visible on MR diffusion-weighted imaging (DWI) in the territory of a single internal carotid artery
• Presence of carotid artery plaques in the ipsilateral or contralateral carotid artery as defined by ultrasound (criteria: plaque thickness at least 2mm; located within 1cm proximal or distal to the carotid bifurcation)
• Written informed consent

Exclusion Criteria:

• Primary referral to an outside hospital (to avoid recruitment bias)
• DWI positive lesions outside the territory of a single internal carotid artery
• Carotid artery stenosis > 69% (North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria) ipsilateral to the stroke or TIA as defined by ultrasound (systolic peak flow velocity ≥ 300 cm/s)
• Standard contra-indications for MRI
• Documented allergy to MRI contrast media
• History of radiation to the neck area
• Renal clearance < 30 ml/minute
• Creatinine levels > 2 times the upper limit of the standard range of the respective laboratory within the last 30 days prior to MRI
• Surgical procedure within 24 hours preceding the MRI

Patients admitted to a specialized stroke service because of an acute stroke or TIA