Methodological preamble
The velocity thresholds on this page are consensus values derived from studies correlating duplex with angiography. One point on which every scientific society agrees is that each laboratory should ideally validate its own criteria against an angiographic reference, because absolute velocity values depend on the equipment, the insonation angle and the patient's haemodynamic state (cardiac output, contralateral stenosis, arrhythmia, aortic valve disease).
Velocities are expressed in cm/s unless otherwise stated; PSV = peak systolic velocity, EDV = end-diastolic velocity, ratio = the velocity within the stenosis divided by the velocity in a reference segment.
Extracranial cerebrovascular (carotid and vertebral arteries)
What the report must contain
- Equipment and transducer type used.
- B-mode description of the wall and of any plaque: location, extent, echogenicity (homogeneous/heterogeneous), surface (smooth/irregular), any ulceration.
- Luminal diameter of the common carotid artery and of the bulb.
- Intima–media thickness (IMT) where indicated.
- For each segment (CCA, bulb, proximal/distal ICA, ECA, vertebral arteries): PSV and EDV.
- Degree of stenosis as a percentage, specifying the measurement method used (NASCET or ECST).
- ICA/CCA ratio when the stenosis is significant.
- Direction and characteristics of vertebral artery flow.
- Comparison with previous studies at follow-up.
Diagnostic criteria — SRU 2003 consensus (NASCET method)
The most widely used international reference is the 2003 consensus of the Society of Radiologists in Ultrasound, which classifies internal carotid artery stenosis into categories: normal, <50%, 50–69%, ≥70% up to near-occlusion, near-occlusion, occlusion.
| ICA stenosis | ICA PSV | ICA EDV | ICA/CCA ratio | Plaque |
|---|---|---|---|---|
| Normal | <125 | <40 | <2.0 | None |
| <50% | <125 | <40 | <2.0 | <50% diameter |
| 50–69% | 125–230 | 40–100 | 2.0–4.0 | ≥50% diameter |
| ≥70% (up to near-occlusion) | >230 | >100 | >4.0 | ≥50% diameter |
| Near-occlusion | variable/low | variable | variable | String-like lumen |
| Occlusion | absent | absent | — | No flow |
PSV and EDV in cm/s. PSV and the presence of plaque are the primary parameters; EDV and the ratio are secondary confirmatory parameters. In near-occlusion velocities may paradoxically fall: the diagnosis rests on B-mode and colour Doppler.
NASCET and ECST: mind the method
Two methods exist for measuring carotid stenosis, and they give different values for the same vessel. The European ESVS 2023 guidelines record the approximate equivalence: 50% NASCET corresponds to roughly 75% ECST, and 70% NASCET to roughly 85% ECST. Always stating the method avoids wrongly including or excluding patients from revascularisation criteria.
Lower extremity arterial
What the report must contain
- Equipment and transducer type.
- For each segment (iliac, common femoral, profunda femoris, superficial femoral, popliteal, tibial and peroneal arteries): wall profile, diameter, PSV.
- Doppler waveform morphology: triphasic (normal), biphasic, monophasic; presence of a tardus-parvus pattern downstream of a stenosis.
- Location, extent (length in cm) and percentage grade of every stenosis.
- Velocity ratio (PSV within the stenosis / PSV in the normal proximal segment).
- Sites of occlusion and collateral pathways of reconstitution.
- Status of any bypass graft or stent (patency, velocities).
Diagnostic criteria — velocities and ratio (University of Washington criteria)
The degree of stenosis rests principally on the velocity ratio (PSV within the stenosis divided by PSV in the normal proximal segment) and on the rise in PSV. The ratio is more reliable than the absolute value alone because it is independent of cardiac output.
| Stenosis grade | Velocity ratio | Doppler waveform |
|---|---|---|
| Normal | <1.5 | Triphasic, normal PSV |
| 30–49% | 1.5–2.0 | Triphasic or biphasic |
| 50–75% | 2.0–4.0 | Monophasic, spectral broadening |
| >75% | >4.0 | Monophasic, marked broadening |
| Occlusion | — | No flow; tardus-parvus waveform downstream |
As an operational summary (StatPearls / Society for Vascular Medicine): a ratio >2 indicates >50% stenosis, a ratio >4 indicates >75–80% stenosis. Beyond 95% stenosis velocity paradoxically falls: the diagnosis must be confirmed with B-mode and colour Doppler.
The Italian approach
The SIAPAV guidelines on chronic obstructive peripheral arterial disease and the SIDV-GIUV templates require, for each segment, a description of profile, wall and diameter, the presence of stenosis with the percentage diameter reduction, and the length in centimetres. The Italian percentage is traditionally referred to the diameter reduction of the vessel at the level of the stenosis.
Lower extremity venous
What the report must contain
- Patient position during the examination (reflux must be assessed standing or in reverse Trendelenburg, not supine).
- Patency and compressibility of the deep venous system; sequelae of any previous thrombosis.
- Competence of the saphenofemoral and saphenopopliteal junctions, with location and diameter.
- Extent of reflux in the great and small saphenous veins at thigh and calf level, with diameters.
- Number, location, diameter and competence of incompetent perforating veins.
- Other refluxing veins and the source of filling of the varicosities.
- Hypoplastic, atretic, absent or previously stripped veins.
- CEAP clinical classification where requested.
Diagnostic criteria — reflux duration (UIP consensus)
The consensus document of the Union Internationale de Phlébologie (UIP) defines pathological reflux as retrograde flow lasting longer than the thresholds below, elicited by compression–release or Valsalva manoeuvres.
| Venous segment | Pathological reflux duration |
|---|---|
| Femoral and popliteal veins (deep) | > 1.0 s |
| Great and small saphenous, superficial veins | > 0.5 s |
| Perforating veins | > 0.35 s |
| Tibial and deep muscular veins | > 0.5 s |
General reference threshold: reflux > 0.5 s (Labropoulos et al., J Vasc Surg 2003). Large-calibre deep veins tolerate a longer physiological reflux, hence the 1 s threshold; perforators carry the lowest threshold.
The Italian approach and recent references
The SIDV-GIUV templates for the venous system require complete mapping of the saphenous trunks, junctions and perforators with their diameters, integrated with the CEAP classification. The most up-to-date international reference is the SVS-AVF-AVLS 2022 guideline on the management of varicose veins, which confirms duplex ultrasound as the first-line study for superficial truncal reflux.
Arteriovenous fistulae for haemodialysis
What the report must contain
- Type of access (radiocephalic, brachiocephalic, brachiobasilic) and date of creation.
- Inflow artery: diameter, PSV, waveform morphology (low resistance in a mature, functioning fistula).
- Anastomosis: diameter, presence and site of stenosis.
- Outflow vein: diameter, depth from the skin, course, presence of stenosis or of collateral branches diverting flow.
- Access flow volume (Qa), usually measured in the brachial artery.
- Central venous outflow as far as it can be assessed.
- Presence of thrombosis, aneurysm/pseudoaneurysm, fluid collections.
Maturation criteria — the "rule of 6"
Whether a fistula is mature and usable for dialysis is judged against reference parameters commonly summarised as the "rule of 6":
- Access flow volume (Qa) > 600 mL/min;
- Outflow vein diameter > 6 mm;
- Vein depth from the skin < 6 mm;
- An adequate straight segment of vein available for cannulation (usually several centimetres).
Diagnostic criteria for stenosis
| Parameter | Value suggesting significant stenosis |
|---|---|
| Velocity ratio (SVR) across the stenosis | > 2.0 – 3.0 → ≥50% |
| Diameter reduction (B-mode) | > 50% |
| Access flow volume (Qa) | < 500–600 mL/min, or a fall >25% |
| Associated clinical signs | Loss or reduction of thrill, high venous pressures on dialysis, recirculation |
SVR = the ratio of PSV within the stenosis to PSV in the upstream segment. An SVR >2 with >50% diameter reduction points to a haemodynamically significant stenosis; the finding must always be read together with the flow volume and the clinical picture on dialysis.
Abdominal aorta
What the report must contain
- Maximum aortic diameter, stating the plane of measurement (anteroposterior, transverse) and the caliper method (outer-to-outer, inner-to-inner or leading edge).
- Level of the maximum diameter (infrarenal in most cases).
- Extent of any aneurysm and its relationship to the renal arteries (proximal neck).
- Involvement of the iliac arteries, with their diameters.
- Presence of mural thrombus, dissection, signs of impending rupture.
- Comparison with previous studies (growth rate).
Definitions and intervention thresholds
An abdominal aorta is defined as aneurysmal when the diameter is ≥ 30 mm (or shows an increase of ≥50% over the expected normal calibre). The threshold for considering elective repair is broadly ≥ 55 mm in men and ≥ 50 mm in women, or rapid growth (> 5 mm in 6 months), or the onset of symptoms.
Surveillance intervals — ESVS 2024 and SVS
| Diameter | Interval (men) | Interval (women) |
|---|---|---|
| 25–29 mm (sub-aneurysmal) | every 5 years | every 5 years |
| 30–39 mm | every 3 years | every 3 years |
| 40–44 mm | every 12 months | every 12 months |
| 45–49 mm | every 12 months | every 6 months |
| ≥ 50 mm | every 6 months | consider repair |
A synthesis of ultrasound surveillance intervals according to ESVS 2024 and SVS 2018, to be adjusted for life expectancy, fitness for future intervention and patient preference. The SVS suggests 12-monthly surveillance for 40–49 mm and 6-monthly for 50–54 mm.
Visceral vessels (mesenteric and renal)
What the report must contain
- Aortic PSV at the level of the origin of the superior mesenteric artery (the denominator for the ratios).
- Coeliac axis, superior (SMA) and inferior (IMA) mesenteric arteries: PSV, EDV, waveform morphology; for the coeliac axis, variation with respiration (median arcuate ligament compression).
- Main renal arteries: PSV at the origin and along the course, EDV, renal–aortic ratio (RAR).
- Intrarenal parameters: resistive index (RI), acceleration time, tardus-parvus pattern in the interlobar vessels.
- Renal length (asymmetry).
- Status of any stent (thresholds differ from native vessels).
Diagnostic criteria — mesenteric arteries
| Vessel | Stenosis | Criterion |
|---|---|---|
| Coeliac axis | ≥ 70% | PSV ≥ 200 cm/s |
| Superior mesenteric artery | ≥ 70% | PSV ≥ 275 cm/s |
| Inferior mesenteric artery | > 50% | PSV > 200 cm/s (or ≥ 250) |
Summarised from Kupinski (Vasc Med 2023). For the coeliac axis the dynamic component related to the median arcuate ligament must always be assessed (compression in expiration). For stents the thresholds are higher (for example coeliac stent PSV ≥ 370 cm/s per SVS guidance).
Diagnostic criteria — renal arteries
| Parameter | Threshold for ≥ 60% stenosis |
|---|---|
| Renal artery PSV | > 180–200 cm/s |
| Renal–aortic ratio (RAR) | > 3.5 |
| Intrarenal acceleration time | > 0.07 s (indirect) |
| Interlobar waveform | tardus-parvus (indirect) |
| Occlusion | No flow + low parenchymal signal |
For the RAR to be usable, the reference aortic PSV must lie between 40 and 100 cm/s. A RAR >3.5 is associated with >60% stenosis (sensitivity ~91%, specificity ~95%, Kohler et al.). Some laboratories prefer PSV alone, on the grounds that the RAR is affected by the variability of aortic velocity.
Cross-territory summary
An overview of the principal parameters by territory, as a quick reminder. The values must be read in the light of the methodological preamble: they are consensus thresholds, not absolute truths.
| Territory | Key parameter | Reference threshold |
|---|---|---|
| Internal carotid ≥70% | PSV / EDV / ratio | >230 / >100 / >4.0 |
| Lower extremity arterial >50% | velocity ratio | >2.0 |
| Lower extremity venous | reflux duration (superficial) | >0.5 s |
| AV fistula — stenosis | SVR + diameter | >2.0 + >50% reduction |
| AV fistula — maturation | flow volume / vein diameter | >600 mL/min / >6 mm |
| Aorta — aneurysm | maximum diameter | ≥30 mm |
| Renal ≥60% | PSV / RAR | >180–200 / >3.5 |
| Superior mesenteric ≥70% | PSV | ≥275 cm/s |
Sources
The principal sources used for this synthesis. For exact values and full context, please refer to the original documents.
- Carotid. Grant EG et al. Carotid artery stenosis: gray-scale and Doppler US diagnosis — SRU Consensus Conference. Radiology 2003. — ESVS 2023 Clinical Practice Guidelines on Atherosclerotic Carotid and Vertebral Artery Disease (esvs.org). — SIDV-GIUV, guidelines for vascular diagnostics (sidv.net). — SICVE-CNEC, guideline on obstructive carotid disease.
- Lower extremity arterial. University of Washington duplex criteria. — StatPearls, Peripheral Arterial Duplex Assessment (NCBI). — Society for Vascular Medicine, Arterial Duplex Ultrasonography. — SIAPAV, guidelines on obstructive peripheral arterial disease.
- Lower extremity venous. Coleridge-Smith P et al. UIP Consensus Document, Part I–II (Eur J Vasc Endovasc Surg 2006). — Labropoulos N et al. Definition of venous reflux (J Vasc Surg 2003). — SVS/AVF/AVLS 2022 Guidelines for varicose veins.
- Arteriovenous fistulae. Ultrasound diagnosis of access stenosis (MDPI Diagnostics 2022). — Studies developing duplex criteria for AV fistula stenosis (J Vasc Surg).
- Abdominal aorta. ESVS 2024 Guidelines on Abdominal Aorto-Iliac Artery Aneurysms. — SVS 2018, Care of Patients with Abdominal Aortic Aneurysm (vascular.org).
- Visceral vessels. Kupinski AM. Mesenteric and renal arterial duplex ultrasound: a review (Vasc Med 2023). — ESVS 2025 Clinical Practice Guidelines on Mesenteric and Renal Artery/Vein Disease.