Innovative Applications of Ultrafast Ultrasound Imaging in Peripheral Vascular Pathology: Evaluation of Carotid Plaque Vulnerability by Quantification of Neovascularization

Stroke is the second leading cause of death in the Western world and the leading cause of major lifelong disability. About 15% of strokes are secondary to thrombosis or embolization of an unstable atheromatous carotid plaque. In these symptomatic patients, the degree of carotid stenosis is correlated with the risk of early recurrence. Patients with stenosis over 70% are therefore offered an endarterectomy, an operation to remove carotid plaque, to prevent future strokes[1]. In asymptomatic patients, the degree of stenosis is a limited predictor, and better risk stratification is required to assess the degree of plaque vulnerability and stroke risk of the patient. The therapeutic decision towards endarterectomy in addition to drug therapy is debated because of a variable and dependent benefit/risk balance for each patient. A number of imaging parameters have been studied: ulceration, heterogeneity, vascularization of the plaque for example, but their place is not well defined [2].

The usual evaluation of carotid stenosis is by conventional Doppler ultrasound with calculation of the degree of stenosis according to the NASCET criteria.

For symptomatic stenoses the intervention is recommended when above 70% and is discussed from 50% to 70% of NASCET stenosis degree.

For asymptomatic stenoses, the procedure is discussed when above 60% taking into account the patient's life expectancy, the risk of the surgery and the unstable nature of the plaque [2].

Destabilization of the carotid plaque is partially induced by inflammation associated with neo-vascularization. The detection of these new vessels by conventional contrast ultrasound has already shown a distinction between stable and unstable plaques, by the presence or absence of microbubbles in the plaque. However, this assessment is not very precise and only the most vascularized plaques can be detected. Ultrafast ultrasound Imaging is a new ultrasonic Imaging modality that allows detecting low speed flows, a tiny vascular structure within the vessel wall.

RESEARCH HYPOTHESIS Plaques neo-vascularization would be more precisely detected and characterized by ultrafast imaging coupled with microbubble injection than conventional ultrasound imaging.

A better assessment of plaque instability could improve the selection of patients for carotid endarterectomy and increase the benefit/risk ratio of this preventive surgery.