How to Read and Interpret Carotid Ultrasound Results

A carotid ultrasound report typically includes velocity measurements, a stenosis grade, plaque descriptions, and sometimes an intima-media thickness value. These results, taken together, tell your doctor how freely blood flows through the carotid arteries in your neck and whether plaque buildup poses a risk for stroke. The report can look dense and technical, but the core findings boil down to a few key numbers and categories that are straightforward once you know what they represent.

What the Ultrasound Is Actually Doing

A carotid ultrasound uses three overlapping techniques during a single exam, and your report reflects data from all three. The first is standard grayscale imaging, sometimes called B-mode, which produces a live picture of the artery walls and any plaque sitting inside them. This is the mode used to measure the thickness of the artery wall and to describe what plaque looks like. The second technique layers color over that grayscale image to show the direction and relative speed of blood flow. The third, called spectral or pulse-wave Doppler, places a tiny measurement cursor inside the artery and records the precise speed of blood at that point, producing the waveform tracings you may see printed in your report.

Each technique answers a different question. Grayscale imaging shows the anatomy and plaque structure. Color Doppler flags areas where flow is disrupted or absent. Spectral Doppler gives the hard numbers that determine a stenosis grade. When your report lists a “peak systolic velocity” or “end-diastolic velocity,” those come from the spectral Doppler measurement.

Understanding Velocity Measurements

The single most important number on a carotid ultrasound report is the peak systolic velocity, or PSV, of the internal carotid artery. This is the fastest speed blood reaches during each heartbeat, measured in centimeters per second. When an artery narrows, blood has to squeeze through a smaller opening, and it speeds up the same way water speeds up when you put your thumb over a garden hose. A higher PSV means a tighter narrowing.

Your report will also list the end-diastolic velocity (EDV), which is the speed of blood at the slowest point between heartbeats. In mild narrowing, EDV stays relatively normal. It starts climbing when stenosis becomes more severe, so a high EDV is a red flag that the blockage is significant. Many labs also calculate a ratio between the PSV in the internal carotid artery and the PSV in the common carotid artery just below it. This ratio helps correct for person-to-person differences in overall blood flow speed.

The angle at which the ultrasound beam hits the flowing blood matters enormously. For accurate velocity readings, the beam needs to meet the blood flow at an angle between roughly 30 and 60 degrees. At steeper or shallower angles, the physics of the measurement breaks down and the speed reading becomes unreliable. UK joint reporting guidelines recommend keeping this angle between 45 and 60 degrees for all velocity measurements.

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Stenosis Grades and What They Mean

Your report will categorize the narrowing of each internal carotid artery into a grade. Most labs in North America follow criteria established by the Society of Radiologists in Ultrasound (SRU), which maps velocity cutoffs to categories defined by a landmark surgical trial called NASCET.

⁴ The typical categories look like this:

Normal: No significant narrowing. PSV in the internal carotid artery is below about 125 cm/s, and no plaque is visible.
Mild (1–49%): Some plaque is present, but velocities remain below the threshold that signals hemodynamically significant disease. Blood flow is not meaningfully restricted.
Moderate (50–69%): The artery has lost at least half its diameter. PSV is elevated, and the ratio between internal and common carotid velocities begins to climb. This is the range where clinicians start discussing whether intervention makes sense, especially if you have had stroke symptoms.
Severe (70–99%): The artery is critically narrowed. PSV is usually well above 230 cm/s, EDV is elevated, and the velocity ratio is high. This grade carries the highest stroke risk and is the range where surgery or stenting is most clearly beneficial in symptomatic patients.
Occlusion: No detectable flow. The artery is completely blocked. The report may note absent color flow and no spectral Doppler signal.

Different countries use slightly different grading systems. The German Society of Ultrasound in Medicine (DEGUM) uses a revised multiparametric approach that incorporates additional measurements alongside PSV, though both systems map findings back to the same NASCET-based categories.

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One ongoing debate worth knowing about: some researchers have found that the standard SRU velocity cutoff for 50% stenosis, a PSV of 125 cm/s, may be too sensitive, meaning it flags some arteries as moderately narrowed when they are not. A higher threshold of around 180 cm/s has been proposed for greater accuracy at that grade, though the evidence is not yet strong enough to change the criteria for higher-grade stenosis.

Intima-Media Thickness

Some reports include a measurement called intima-media thickness, or IMT. This is the combined thickness of the two innermost layers of the artery wall, measured in millimeters on the grayscale image. It is typically assessed on the far wall of the common carotid artery, where the measurement is most reproducible.

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A thicker wall signals earlier-stage atherosclerosis, even before discrete plaque forms. In a large study from the Framingham Offspring cohort, each standard-deviation increase in the maximum IMT of the internal carotid artery was associated with about a 21% higher risk of cardiovascular events.

⁷ That said, the predictive value of IMT alone, measured only at the common carotid artery, adds only a small amount of information beyond what your doctor already knows from standard risk factors like blood pressure and cholesterol. Adding IMT measurements from the carotid bulb and internal carotid artery, or simply noting whether plaque is present at all, improves stroke and heart attack prediction much more.

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If your report includes an IMT value, a reading under about 0.9 mm at the common carotid artery is generally considered normal for middle-aged adults, though the number rises with age. The more useful takeaway from the IMT section of a report is often the trend: is the wall getting thicker over repeated scans, or has it stabilized with treatment?

What the Plaque Description Tells You

Beyond how much the artery is narrowed, your report may describe what the plaque itself looks like. This matters because not all plaques are equally dangerous. A hard, calcified plaque that has been stable for years poses less immediate stroke risk than a soft, irregular plaque with an ulcerated surface, even if they produce similar degrees of narrowing.

Reports typically describe plaque using echogenicity, which is how bright or dark the plaque appears on the grayscale image. Bright, echogenic plaque is usually calcified and relatively stable. Dark, hypoechoic plaque tends to be fatty or hemorrhagic and is more prone to rupture. Research has found that plaques with a larger proportion of low-intensity gray areas on ultrasound are associated with symptoms like transient ischemic attacks or stroke.

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Your report may also note whether the plaque surface is smooth, irregular, or ulcerated. Ulceration is a particular concern. In one study comparing symptomatic and asymptomatic arteries, plaque ulceration was present in half of the arteries that had caused symptoms but only about 10% of those that had not.

⁹ An ulcerated plaque has a crater-like defect on its surface where pieces can break off and travel to the brain.

Some newer techniques push plaque assessment further. Contrast-enhanced ultrasound uses microbubble contrast agents injected into a vein to highlight tiny new blood vessels growing inside the plaque, a process called intraplaque neovascularization. These fragile new vessels are a hallmark of vulnerable plaque because they can leak or rupture, destabilizing the plaque from within.

¹⁰ ¹¹ Contrast-enhanced studies are not part of routine screening, but your report may reference them if your doctor ordered a more detailed assessment of a known plaque.

Pitfalls That Can Make Results Misleading

Carotid ultrasound is a good first-line test, but certain situations can produce results that over- or underestimate the true degree of stenosis. Knowing these pitfalls helps you understand why your doctor might order additional imaging or interpret your results with caveats.

Heavy calcification is the biggest culprit. When plaque is densely calcified, it blocks the ultrasound beam and creates an acoustic shadow behind it, essentially a blind spot. In a study of patients with significant acoustic shadowing, the standard velocity measurements correlated only weakly with the degree of stenosis found on CT angiography, and the sensitivity of ultrasound for detecting severe stenosis dropped to as low as 23–33%.

¹² If your report notes significant calcification or acoustic shadowing, the stenosis grade should be considered less reliable.

Vessel tortuosity is another issue, especially in older adults. When the carotid artery twists or kinks, the ultrasound beam may strike the blood flow at an inaccurate angle, producing velocity readings that are artificially high or low.

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A subtler confounder is what is happening on the opposite side. When one carotid artery is severely narrowed, the other side compensates by carrying more blood, which raises its velocity. In patients with severe contralateral stenosis of 70% or greater, the PSV on the measured side was artificially elevated by an average of 84 cm/s. That is enough to push a moderate stenosis reading into the severe category on paper.

¹⁴ A skilled interpreting physician will look at both sides together and account for this effect, but it is worth understanding if your report shows high velocities on one side and severe disease on the other.

When Confirmatory Imaging Is Recommended

For mild disease, carotid ultrasound alone is sufficient. But when the stenosis reaches the moderate-to-severe range where surgical decisions are on the table, most guidelines recommend confirming the finding with a second imaging method. CT angiography and MR angiography provide a different view of the artery and are not affected by calcification or angle errors in the same way.

A retrospective study comparing duplex ultrasound with CT angiography in stroke patients concluded that anyone showing 50% or greater stenosis on ultrasound should have the finding verified with CT angiography before treatment decisions are made.

¹⁵ This is standard practice, not a sign that something went wrong with your ultrasound. Carotid ultrasound is the screening tool; cross-sectional imaging is the confirmatory step for high-stakes decisions.

How Results Translate to Treatment Decisions

The relationship between your ultrasound results and what happens next depends heavily on whether you have had symptoms. In this context, “symptomatic” means you have experienced a stroke, a transient ischemic attack, or vision loss on the same side as the narrowed artery.

European guidelines set a threshold of 70% stenosis for a formal recommendation of revascularization (surgery or stenting) in symptomatic patients. At 50–69% stenosis with symptoms, revascularization is discussed on a case-by-case basis. For asymptomatic patients, the threshold for considering intervention is generally higher, around 60%, though the trend in recent evidence has been toward favoring modern medical therapy as the foundation for managing asymptomatic carotid stenosis.

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A meta-analysis of the most recent major trials for asymptomatic carotid stenosis reinforced that contemporary medical therapy, meaning aggressive management of blood pressure, cholesterol, blood sugar, and lifestyle factors, remains the primary treatment for most people with asymptomatic narrowing. Revascularization is reserved for carefully selected patients after individualized risk assessment.

¹⁷ This means that even a report showing significant stenosis does not automatically lead to surgery. The decision integrates your symptoms, the plaque characteristics, your overall health, and how well your risk factors are controlled.

Vertebral Artery Findings

Most carotid ultrasound exams also include a quick look at the vertebral arteries, which run alongside the cervical spine and supply the back of the brain. Your report may note whether vertebral artery flow is normal and in the expected direction.

Reversed vertebral artery flow is a distinctive finding that suggests subclavian steal syndrome, a condition where a blockage in the subclavian artery (which feeds the arm) causes blood to flow backward down the vertebral artery to bypass the blockage. In one case report, reversed flow in the left vertebral artery prompted the diagnosis of subclavian steal alongside bilateral carotid stenosis.

¹⁸ If your report mentions reversed vertebral flow, your doctor will likely investigate the subclavian artery and possibly order further imaging.

Monitoring After Surgery or Stenting

If you have had a carotid endarterectomy or stent placement, follow-up ultrasounds are used to watch for restenosis, which is the artery narrowing again at or near the treatment site. In a study tracking patients after stenting, duplex ultrasound was performed every three months for two years. Most patients remained free of significant restenosis, but a small number developed recurrent narrowing ranging from 60% to 80%, one of whom became symptomatic.

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Post-procedure velocity criteria may differ slightly from the standard thresholds used for native arteries. A stented artery has different wall compliance than a normal one, and velocity cutoffs validated for unstented arteries do not always translate cleanly. Your vascular lab should note whether modified criteria are being applied. If your follow-up report shows rising velocities over successive exams, that trend matters more than any single snapshot.

Artificial Intelligence and the Future of Interpretation

Interpreting plaque vulnerability from an ultrasound image involves a degree of subjectivity: different readers may characterize the same plaque differently. This is one reason AI-assisted interpretation has become an active research area. Machine learning algorithms trained on large datasets of ultrasound images can learn to recognize patterns associated with vulnerable plaques, potentially making assessments more consistent and reproducible across different labs and operators.

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These tools are not yet standard in clinical practice. Current AI applications focus primarily on plaque classification and risk stratification rather than replacing the velocity-based stenosis grading that drives treatment decisions. For now, the human interpreting physician remains the final reader of your exam. But if you see an AI-assisted analysis mentioned on a future report, it is serving as a second set of eyes for plaque characterization rather than replacing the conventional measurements described above.

1
Annals of Clinical Neurophysiology. Carotid duplex ultrasound: interpretations and clinical applications
2
Europe PMC. General principles of carotid Doppler ultrasonography
3
PubMed Central. Joint recommendations for reporting carotid ultrasound investigations in the United Kingdom
4
Wiley Online Library. Accuracy of the Society of Radiologists in Ultrasound (SRU) Carotid Doppler Velocity Criteria for Grading North American Symptomatic Carotid Endarterectomy Trial (NASCET) Stenosis: A Meta-Analysis
5
Thieme Connect / Ultraschall in der Medizin. Ultrasonography Grading of Internal Carotid Artery Disease: Multiparametric German Society of Ultrasound in Medicine (DEGUM) versus Society of Radiologists in Ultrasound (SRU) Consensus Criteria
6
ScienceDirect / Elsevier. Carotid intima-media thickness and plaque in cardiovascular risk assessment
7
Massachusetts Medical Society. Carotid-wall intima-media thickness and cardiovascular events
8
American Journal of Roentgenology. Carotid Plaque Vulnerability Assessment Using Ultrasound Elastography and Echogenicity Analysis
9
PubMed Central. Asymptomatic bruit, carotid and vertebrobasilar transient ischemic attacks–a clinical and ultrasonic correlation
10
Elsevier. The updated roles of new ultrasound imaging techniques in assessing carotid vulnerable plaques
11
Europe PMC. Contrast-Enhanced Ultrasound Feasibility in Assessing Carotid Plaque Vulnerability-Narrative Review
12
PubMed Central. Acoustic shadowing impairs accurate characterization of stenosis in carotid ultrasound examinations
13
PubMed Central. A method to detect tortuosity of vessel using non imaging ultrasound approach in carotid structure
14
PubMed Central. Effect of contralateral carotid artery stenosis on carotid ultrasound velocity measurements
15
PMC. Comparison of Doppler Ultrasound and Computerized Tomographic Angiography in Evaluation of Cervical Arteries Stenosis in Stroke Patients, a Retrospective Single-Center Study
16
Oxford Academic. Management of carotid stenosis for primary and secondary prevention of stroke: state-of-the-art 2020: a critical review
17
PubMed Central. Modern Management of Asymptomatic Carotid Stenosis: A Meta-Analysis of CREST-2, SPACE-2, and ECST-2
18
Elsevier / Annals of Medicine and Surgery. Diagnosis and management of unilateral subclavian steal syndrome with bilateral carotid artery stenosis
19
Europe PMC. Restenosis after carotid endarterectomy: incidence and endovascular management
20
Elsevier. Advances in the Application of Artificial Intelligence in the Ultrasound Diagnosis of Vulnerable Carotid Atherosclerotic Plaque