Rationale: Approximately 15-20% of strokes originates from an atherosclerotic plaque rupture in the carotid artery. To reduce the risk of stroke, patients should be evaluated for possible carotid endarterectomy (CEA), which is based on simple geometrical and clinical measures. Multiple studies have shown that the current risk stratification may lead to both over- and under-treatment for patients with carotid artery stenosis. This implicates that the current guidelines are lacking patient-specific parameters and have limited sensitivity. There is a wealth of evidence implicating the important role of local (disturbed) blood flow throughout the onset and progression of atherosclerosis. Novel flow-related measures, that go beyond simple geometrical indications, are required to improve diagnosis and treatment in patients with carotid artery stenosis. Nowadays, ultrasound (US) is one of the main techniques to assess for the presence and extent of carotid artery stenosis. However, current clinically-used US systems are unable to acquire and visualize the complex flow phenomena that play such a crucial role in the atherosclerotic disease process. With the advent of ultrafast ultrasound imaging, acquiring thousands of images per second, continuous tracking of flow in all directions became feasible, which enables us to image two-dimensional blood flow and possible disturbances with high accuracy and precision.

In this project, we aim to assess whether flow (related) parameters are associated with disease progression (and if so, which), in order to map the progression of atherosclerotic plaques using non-invasive, US-based blood flow imaging. In the future, this could improve risk stratification for individual patients for surgery, decrease patient mortality and morbidity, and therefore reduce healthcare costs.

Objective: To longitudinally assess the association between spatio-temporal blood flow velocities (peak systole and end-diastole at common carotid artery, maximum stenosis and internal carotid artery) and the progression of carotid atherosclerosis defined by duplex measurements.

Secondary objectives are to investigate the association between blood flow-derived parameters, including wall shear stress (WSS), vector complexity and vorticity, and the progression of atherosclerosis defined by duplex measurements. Furthermore, to assess the association between spatio-temporal blood flow velocities and blood flow-derived parameters (WSS, vector complexity and vorticity) and the progression of atherosclerosis as measured using ultrasound-based strain imaging.

Inclusion Criteria:

• Adult male or female (≥18 years old);
• Informed consent form understood and signed, and patient agrees to follow-up visits;
• Presence of carotid artery stenosis (between 30%-69%) according to conventional duplex measurements (peak-systolic velocity of 125-230 cm/s [5] in combination with visible lumen reduction >30% according to North American Symptomatic Carotid Endarterectomy Trial [NASCET] method);
• Defined asymptomatic with respect to the ipsilateral carotid artery stenosis.

Exclusion Criteria:

• A planned carotid revascularisation for the ipsilateral carotid artery stenosis at date of inclusion;
• History of carotid revascularisation at artery under investigation;
• Visible near occlusion at asymptomatic stenosis side according to conventional duplex measurements;
• Life expectancy < 2 years;
• Participating in another clinical study, interfering on outcomes

Patients with an asymptomatic carotid artery stenosis, defined by 30% to 69% narrowing of the carotid artery according to conventional duplex measurements in the absence of ipsilateral retinal or cerebral ischemia in the preceding 6 months.