Carotid duplex ultrasound combines real-time B-Mode imaging with color and spectral Doppler to evaluate the common carotid artery (CCA), internal carotid artery (ICA), and external carotid artery (ECA) for atherosclerotic plaque, stenosis, and abnormal flow. Peak systolic velocity (PSV) and end-diastolic velocity (EDV) measurements in the ICA, combined with the ICA/CCA velocity ratio, are used to grade stenosis severity according to established criteria. It is the first-line screening test for carotid artery disease in patients with stroke symptoms or bruits.