Informational only. This page describes how this condition appears on ultrasound imaging for educational purposes. It is not medical advice, diagnosis, or treatment guidance.
Carotid artery stenosis is narrowing of the internal carotid artery, almost always from atherosclerotic plaque. It is the imaging finding behind a substantial fraction of strokes and transient ischemic attacks (TIAs), and carotid duplex ultrasound is the front-line modality for detection and grading.
What it is
The carotid arteries supply blood to the brain. Atherosclerotic plaque tends to accumulate at the carotid bifurcation, where flow patterns favor deposition. As plaque builds, the lumen narrows; severe narrowing reduces flow to the brain, and unstable plaque can rupture and embolize, causing a stroke or TIA.
Stenosis is graded by the percentage of luminal narrowing. The clinically meaningful thresholds — particularly the >50% and >70% breakpoints — derive from the NASCET (North American Symptomatic Carotid Endarterectomy Trial) and ACAS trials, which established that surgical or endovascular intervention reduces stroke risk above specific severity cutoffs in symptomatic and asymptomatic patients respectively.
How it appears on ultrasound
Carotid duplex ultrasound combines B-mode imaging of the vessel walls with spectral Doppler measurement of flow velocity. The exam follows a standardized protocol covering the common carotid artery (CCA), the bifurcation, and the proximal internal and external carotid arteries (ICA and ECA) bilaterally.
Stenosis grading is based primarily on velocity measurements. As a vessel narrows, blood accelerates through the stenosis to maintain flow; peak systolic velocity (PSV) in the ICA rises predictably with severity. Society of Radiologists in Ultrasound consensus criteria associate ICA PSV greater than 230 cm/s with stenosis greater than 70%, and PSV greater than 125 cm/s with greater than 50% narrowing. End-diastolic velocity and the ICA-to-CCA velocity ratio refine the grade and are particularly useful in patients with contralateral occlusion or unusual hemodynamics.
B-mode evaluation describes plaque morphology — surface (smooth or irregular), echogenicity (calcified plaques throw acoustic shadows; soft plaque is hypoechoic and considered higher-risk), and any ulceration. Color Doppler highlights flow disturbance and aliasing at the stenosis, helping the sonographer place the spectral gate at the maximum velocity location.
Limitations include heavy calcification, which shadows out the lumen and can prevent direct measurement; tortuous vessels that complicate angle correction; and the operator dependence inherent to all ultrasound. CT angiography or MR angiography is used for confirmation when ultrasound is non-diagnostic or before intervention.
Which specialty images it
Vascular sonography handles all carotid duplex imaging. RVT credential holders perform these exams in vascular labs, hospital imaging departments, and stroke prevention clinics. The vascular specialty page covers the credential, scope of practice, and typical work settings. Radiologists or vascular surgeons interpret the studies.