Atherosclerotic plaque appears on vascular ultrasound as focal thickening or protrusion of the arterial wall into the lumen. Plaque can be classified by echogenicity (echogenic/calcified, hypoechoic/soft, heterogeneous) and surface characteristics (smooth, irregular, or ulcerated). Calcified plaque casts posterior acoustic shadowing. Plaque morphology helps assess stroke risk — hypoechoic or heterogeneous plaques are associated with higher embolic risk than echogenic plaques. Degree of stenosis caused by plaque is quantified using Doppler velocity criteria.