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Figure 1 (A) Example of the region of interest (ROI) used for the measurements of contrast acoustic intensity (AI) of the entire lumen (white line) and central lumen (yellow line). (B) Two-dimensional (2D) imaging of a normal carotid artery in the transverse view and with pulse sequence scheme (PSS) before intravenous microbubbles (MB) injection showing no background imaging, early after MB injection showing the complete luminal vessel opacification, and late after MB injection showing few MB in the central lumen. The time-intensity curve demonstrates the typical quantification of the mean AI in both the entire lumen ROI and the central lumen ROI. The late 50 frames after clearance of free-flowing MB were chosen for the calculation of endothelial AI, defined as the difference between the mean entire lumen AI minus the central lumen AI (see text for details).