Degree of ICA Stenosis: Duplex Velocity Criteria (PSV, EDV, ICA/CCA) vs NASCET/ECST and SRU Consensus
Why the percentage of stenosis is not calculated in 2D mode
The percentage of stenosis (by NASCET or ECST) is an anatomical measurement of the residual lumen relative to the reference diameter, and it is established by imaging methods: digital subtraction angiography (DSA), CT angiography (CTA), or MR angiography (MRA). Do not report the percentage of stenosis obtained by measuring the lumen in 2D mode — this is a limitation of the method, not the task of duplex. The degree of stenosis in duplex is formulated by hemodynamics (velocity + ICA/CCA ratio + EDV + turbulence). If the exact percentage changes the management strategy, confirm it with CTA/MRA.
NASCET vs ECST
The NASCET method compares the stenotic lumen with the normal lumen of the distal ICA, whereas ECST determines the degree of stenosis relative to the original lumen. The use of two different angiographic methodologies initially (NASCET and ECST) became the main source of initial uncertainty in developing valid universal duplex criteria. Modern velocity criteria are derived under the NASCET method — calculate the percentage by NASCET, not mixing with ECST; mixing methods is a common source of “overestimated” stenoses and unjustified surgical decisions. According to ESC 2024 recommendations, using the ECST method for ICA stenosis assessment is not recommended.
Velocity Criteria: SRU and IAC 2021 Modification
The classic SRU 2003 criteria (PSV 125/230) systematically overestimate the degree of stenosis relative to NASCET in practice. The PSV threshold of 125 cm/s for ≥50% is excessively sensitive and insufficiently specific — research data showed that the 125 cm/s threshold does not adequately distinguish ICA lesions below and above 50%. The current IAC 2021 modification raises the threshold for ≥50% to PSV 180 cm/s.
| Degree of ICA Stenosis | PSV (SRUCC) | Additional Criteria |
|---|---|---|
| 50–69% (moderate) | ≥125–230 cm/s (SRUCC); >180 cm/s (Gornik et al.) | PSV >125 cm/s + ICA/CCA >2 |
| ≥70% (severe) | >230 cm/s | With SRUCC criteria — overestimation, consensus absent |
| ≥50% (IAC 2021, current) | PSV raised to 180 cm/s | SRU overestimates degree |
Source data: ESC 2024, Table 10 — Peak systolic velocity criteria for grading ICA stenosis. Ultrasound criteria include threshold values of PSV, EDV, and ICA/CCA PSV ratio.
Decision Based on a Combination of Signs
Velocity increases with the degree of stenosis, but the variability is large even in ICA. Therefore, the degree is determined not by a single PSV, but by a combination: PSV + ICA/CCA ratio + EDV + post-stenotic turbulence + distal effects (tardus-parvus). The ICA/CCA ratio is especially valuable when the absolute velocity is unreliable.
Specific situations: subocclusion may present with low velocity — it cannot be mistaken for normal or occlusion, use sensitive modes. Extensive and tandem stenoses lower PSV — rely on ICA/CCA, turbulence, and distal waveform, measure plaque length; if inconsistent — CTA/MRA (visualizes the entire vessel). In stents, thresholds are higher — apply stent-specific, locally validated criteria.
Requirements for Conclusion (IAC-VT 2024)
IAC-VT (2024) standards require confirming the severity, location, extent, and, if possible, etiology of stenosis with images and spectra in the conclusion, and using velocities, ICA/CCA ratio, spectral shape analysis, and B-mode/color data in interpretation. Distinguish DR (by diameter) and AR (by area): criteria are tied to DR by NASCET; specify the method and technique, not mixing DR with AR. Describe the plaque (echogenicity I–V, surface, ulceration) and geometry (“concentric” or “eccentric”) — morphology clarifies risk beyond percentage.
Frequently asked questions
Can the percentage of stenosis measured in 2D mode be reported in the conclusion?
No. The percentage of stenosis (NASCET/ECST) is an anatomical measurement established by imaging methods (DSA/CTA/MRA). In duplex, the degree is formulated by hemodynamics; measuring the lumen in 2D is a method limitation.
Which calculation method — NASCET or ECST — should be used when comparing with angiography?
NASCET. Velocity criteria are derived under NASCET; mixing with ECST is a common source of overestimated stenoses. According to ESC 2024, ECST is not recommended for ICA stenosis assessment.
Why was the PSV threshold for ≥50% raised in the IAC 2021 modification?
SRU criteria systematically overestimate the degree relative to NASCET, and the PSV threshold of 125 cm/s is excessively sensitive and insufficiently specific. The current IAC 2021 modification raises the threshold for ≥50% to 180 cm/s.
When is the ICA/CCA ratio particularly important?
When the absolute velocity is unreliable, as well as in extensive and tandem stenoses, which lower PSV. In such cases, rely on ICA/CCA, turbulence, and distal waveform.
What to do in case of ICA subocclusion with low velocity?
Low velocity in subocclusion should not be mistaken for normal or occlusion. Use sensitive modes; if inconsistent — CTA/MRA, which visualizes the entire vessel.