Hardening of the neck vessels (carotid arteries) caused by fatty deposits called 'plaques' is a common cause of strokes. Over time plaques can burst or may lead to a severe narrowing (stenosis) of the neck artery. When plaques burst, small clots or fatty particles (called microemboli) break off, block brain vessels and lead to a stroke. Researchers have an incomplete understanding of the processes that cause hardening of the arteries, development of small clots and are unable to predict who will have a stroke. At present, the only ultrasound scan that evaluates circulation in the head and detects these small clots is called the Transcranial Doppler ultrasound. The aim of the study is to test this simple ultrasound technique to see if it can detect signals that may correspond to these small clots or fatty particles. The other objective is to see how repeatable the ultrasound technique is. This may help to identify patients with hardened neck arteries who are at higher risk of a recurrent stroke. This could also potentially improve patients selection to a targeted surgical or future novel pharmacological therapy.

Inclusion Criteria:

• Healthy volunteers with no previous history of cerebrovascular disease and aged over 18 years old.
• Patients with symptomatic cerebrovascular event (stroke, transient ischaemic attack or amaurosis fugax) and image confirmed carotid artery stenosis of >30%. This will include patients scheduled for carotid endarterectomy (>50% for men and >70% for women, by North American Symptomatic Carotid Endarterectomy Trial criteria) or treated conservatively with an optimal medical therapy (if patient declined surgical intervention or is outside surgical criteria for carotid endarterectomy).

Exclusion Criteria:

• Subjects unable to comply with the study procedures such as a severe disabling stroke.
• Inadequate temporal window for Transcranial Doppler assessment.
• Adults with incapacity.

Two cohorts of subjects including healthy volunteers and those with symptomatic carotid artery stenosis will be recruited in different ways. All subjects will undergo basic clinical evaluation prior to participation. In the second cohort, this will include assessment of relevant carotid artery and brain imaging investigations as well.

Healthy volunteers will be recruited from the Centre for Cardiovascular Science at Edinburgh University by the Primary Investigator (PI).

Patients with evidence of an acute neurovascular event (stroke, transient ischaemic attach and retinal ischaemia) due to a symptomatic carotid artery stenosis will be recruited from the acute TIA/Stroke clinics and inpatients at Edinburgh Royal Infirmary by the responsible Consultant Neurologist or Stroke Physician. Once eligible patients are identified at this point PI will recruit subjects into the study.