Ultrafast ultrasonic imaging (UF) offers the possibility of evaluating local flow velocities over an entire 2D image, allowing access to velocity measurements in contact with the arterial wall and to measure the wall shear stress (WSS). Our objective was to evaluate the feasibility of WSS measurement in a prospective series of patients with carotid stenosis.

For this study, a linear probe was used (SL10-2, 7.5MHz, SuperSonic Imagine©). UUI acquisitions last 600ms, started at the foot of the QRS, with 3 tilted plane waves transmits (−10; 0; 10°) for an effective frame rate of 5000Hz. We evaluated the flow velocity in 5 areas of the carotid wall:

– common carotid artery;

– plaque ascent;

– plaque peak;

– plaque descent;

– internal carotid artery (see Figure 1b).

The Wall Shear Stress (WSS) was computed with the vector field speed using the following formula, WSS=μ.δn.v with v the blood velocity, n the normal vector to the vessel wall and μ, the blood viscosity, calculated from the haematocrit value.

48 patients were included in this study. Among them, 25 patients (mean age: 72±5 years), had suitable images of carotid plaque analysis, as a longitudinal visualization of the whole plaque was necessary to perform the measurements of WSS. The mean percentage of stenosis was 75±12% (NASCET). The maximal WSS was variable along the carotid plaque with a progressive increase to a maximum value at the peak (2.12±1.27Pa). The post-stenotic descent zone has the lowest shear stress (0.57±0.39Pa), lower than the WSS values in the healthy zone (1.02±0.36Pa for the common carotid and 0.68±0.39Pa for the internal carotid artery) (Figure 1).

This method allowed the local and direct evaluation of the plaque's wall shear stress. Unlike the global evaluation of speed using conventional Doppler, these measurements make it possible to better characterize the haemodynamic conditions to better identify areas of vulnerability.