Carotid Stenosis Grading: The SRU 2003 Criteria Explained
A practical breakdown of the Society of Radiologists in Ultrasound 2003 consensus criteria for grading internal carotid artery stenosis — what the velocities mean and how to apply them.
Carotid stenosis grading is one of the most important skills in vascular sonography — and one of the most nuanced. The SRU 2003 consensus criteria are the current standard in the United States, and understanding why the thresholds exist is just as important as memorizing the numbers.
Why Velocity-Based Grading?
The internal carotid artery (ICA) is a low-resistance vessel. As plaque builds up and narrows the lumen, blood velocity increases through the stenotic segment — the same way water speeds up through a narrowed hose. Doppler ultrasound measures this acceleration directly.
The SRU 2003 criteria correlate Doppler velocities with degree of stenosis confirmed on catheter angiography, making them clinically validated thresholds, not arbitrary numbers.
The Criteria at a Glance
| Stenosis Grade | ICA PSV | ICA/CCA Ratio | ICA EDV |
|---|---|---|---|
| Normal | < 125 cm/s | < 2.0 | — |
| < 50% | < 125 cm/s | < 2.0 | — |
| 50–69% | 125–230 cm/s | 2.0–4.0 | — |
| ≥ 70% (non-occlusive) | > 230 cm/s | > 4.0 | > 100 cm/s |
| Near-occlusion | High, low, or variable | Variable | Variable |
| Total occlusion | No detectable flow | — | — |
ICA PSV = Internal Carotid Artery Peak Systolic Velocity ICA/CCA Ratio = ICA PSV divided by CCA PSV ICA EDV = Internal Carotid Artery End-Diastolic Velocity
Key Points for the Scan Room
Use the Ratio, Not Just the PSV
Patients with high cardiac output (e.g., anemia, fever, hyperthyroidism) can have elevated ICA PSV without stenosis. The ICA/CCA ratio corrects for this — it compares the ICA velocity to the CCA velocity in the same patient, normalizing for cardiac output.
If the PSV is elevated but the ratio is normal, look for a systemic cause before calling stenosis.
Near-Occlusion Is Tricky
Near-occlusion (>90–99% stenosis) can actually show lower velocities than a 70–79% stenosis because there's so little residual lumen that flow is severely reduced. The vessel may appear thread-like on grayscale, and color Doppler will show a "trickle" of flow.
This is one of the most common pitfalls in carotid interpretation. If the vessel looks severely narrowed on grayscale but the PSV seems low, consider near-occlusion.
Contralateral Disease Affects Velocities
Severe stenosis or occlusion on one side causes compensatory increased flow on the contralateral side. A patient with right ICA occlusion may have falsely elevated left ICA velocities. Always correlate bilaterally.
What to Include in Your Report
When grading carotid stenosis, SonoBuddy's protocol checklist includes:
- Peak systolic velocity (ICA and CCA, bilateral)
- End-diastolic velocity (ICA bilateral)
- ICA/CCA PSV ratio (bilateral)
- Plaque characteristics (echogenicity, surface morphology, length)
- Vertebral artery flow direction and waveform
- Overall impression with stenosis grade per SRU 2003
Using the SonoBuddy Calculator
The built-in Carotid Stenosis Calculator in SonoBuddy takes your ICA PSV, ICA EDV, and CCA PSV, calculates the ratio automatically, and returns the stenosis grade with color-coded severity. It applies the SRU 2003 criteria exactly.
Open SonoBuddy → Calculators → Carotid Stenosis.
Reference: Grant EG, Benson CB, Moneta GL, et al. Carotid artery stenosis: gray-scale and Doppler US diagnosis — Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003;229(2):340-346.
SonoBuddy is a reference tool, not a diagnostic authority.
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