Assessment of carotid plaque score. A). Five segments of the extra-cranial carotid artery: 1. proximal common carotid artery (≥2 cm proximal to carotid bifurcation); 2. distal common carotid artery (<2 cm proximal to carotid bifurcation); 3. carotid bulb and bifurcation; 4. internal carotid artery; and 5. external carotid artery. B). A longitudinal gray-scale image of a carotid plaque in the distal common carotid artery. C). A transverse gray-scale ultrasound image of the carotid plaque in B. The degree of the carotid stenosis is expressed as the percentage reduction of lumen diameter (1-D1/D2 = 41.3%). Carotid plaque score is the summation of the degree of carotid stenosis of the five segments in both carotid arteries.