Brazil: the main reference adopted here is the 2023 DIC/SBC + Brazilian College of Radiology + Brazilian Society of Angiology and Vascular Surgery update, using NASCET grading. United States: IAC 2023 recommends raising the internal carotid systolic velocity threshold to 180 cm/s for 50% stenosis. When standards diverge, the interface marks yellow and names the source.
Measurements and reference values
Measurement
Usual value
Note
Peak systolic velocity — internal carotid artery
<140 in the Brazilian standard for <50% cm/s
IAC 2023 uses <180 cm/s for normal or <50%; 140–179 cm/s is a yellow zone if other parameters do not confirm stenosis.Green — no plaque and low velocity: <125–140 cm/sYellow — SRU/Brazil/IAC divergence: 125–179 cm/sRed — likely hemodynamic stenosis: ≥180 cm/s com placa/razão elevada; >230 cm/s alto grauSource: DIC/SBC-CBR-SBACV 2023 / IAC 2023 / SRU 2003
End-diastolic velocity — internal carotid artery
<40 cm/s
Helps confirm the stenosis range when systolic velocity is not representative.Green: <40 cm/sRed — 50% or more: ≥40 cm/sRed — high grade: >100 cm/s; >140 cm/s sugere 80–89% no padrão brasileiroSource: DIC/SBC-CBR-SBACV 2023 / SRU 2003
Internal carotid / common carotid systolic ratio
<2,0
Use the highest internal carotid systolic velocity at the stenosis and the common carotid systolic velocity in a representative segment away from plaque.Green: <2,0Red — 50–69%: 2,0–4,0Red — 70% or more: >4,0Source: DIC/SBC-CBR-SBACV 2023 / IAC 2023 / SRU 2003
Intima-media thickness
≤0,9 mm
Operational cutoff; the Brazilian recommendation prefers age-, sex- and ethnicity-specific percentiles when available and does not recommend routine measurement in the general population.Green — usual: ≤0,9 mmYellow — thickened: >0,9 mmRed — plaque by thickness: >1,5 mm se focalSource: DIC/SBC-CBR-SBACV 2023 / SBC vascular ultrasound 2019 / Mannheim
Carotid plaque — definition
protrusion ≥0.5 mm or >50% of adjacent wall or >1.5 mm
Any one criterion is enough; plaque should not be called only intima-media thickening.Green: no focal protrusionYellow: smooth/calcified plaque without relevant stenosisRed: ulcerated, predominantly echolucent plaque or stenosis ≥50%Source: DIC/SBC-CBR-SBACV 2023 / Mannheim / Plaque-RADS 2024
Doppler angle for velocities
≤60 degrees
The angle should be corrected and no greater than 60 degrees whenever velocity is measured.Source: CBR technical ultrasound guideline / ACR-AIUM-SPR-SRU cerebrovascular parameter
Classifications and calculators
Quick calculator — carotid stenosis by Doppler
Color
Result
How to interpret
Green
No hemodynamically significant stenosis
Low velocities, internal/common ratio <2.0 and no relevant plaque.
Yellow
Borderline or divergent zone
Plaque without relevant stenosis, intima-media thickening, or velocity 125–179 cm/s without confirmation by ratio/plaque.
Red
Abnormal stenosis or high risk
Stenosis of 50% or more, near occlusion, occlusion, ulcerated plaque or predominantly echolucent plaque.
The calculator cross-checks DIC/SBC-CBR-SBACV 2023, IAC 2023 and SRU 2003. The final result must consider technique, Doppler angle, arrhythmia, tandem stenoses, contralateral occlusion and clinical correlation.
No intraplaque hemorrhage, cap rupture or intraluminal thrombus.
Yellow — low-risk plaque, but not a normal wall.
3a
Maximum wall or plaque thickness ≥3 mm.
Thick/intact fibrous cap; no complicated feature.
Yellow — intermediate risk.
3b
Maximum thickness ≥3 mm with suspected thin fibrous cap.
Ultrasound may suggest it; MRI better assesses a thin cap.
Yellow — possible vulnerability; confirm in context.
3c
Ulcerated plaque.
Cavity/ulcerated surface communicating with the lumen.
Red — abnormal risk morphology.
4a
Intraplaque hemorrhage.
Complicated feature; ultrasound may be limited.
Red — complicated plaque.
4b
Fibrous cap rupture.
Complicated feature.
Red — complicated plaque.
4c
Intraluminal thrombus.
Complicated feature.
Red — complicated plaque.
Plaque-RADS complements, but does not replace, stenosis percentage. When multiple plaques are present, record the highest category and describe the dominant plaque.
Source: Saba et al., JACC Cardiovascular Imaging 2024 / QIMS 2026 ultrasound validation
Internal carotid stenosis — Brazil 2023 (NASCET)
Stenosis
Internal systolic velocity
Internal diastolic velocity
Internal/common systolic ratio
Comment
<50%
<140
<40
<2,0
Not hemodynamically significant; if plaque is present, describe morphology.
50–59%
140–230
40–69
2,0–3,1
Range where there is divergence from IAC 2023 when systolic velocity is below 180 cm/s.
60–69%
no own cutoff
70–100
3,2–4,0
Use diastolic velocity and ratio as confirmation.
70–79%
>230
>100
>4,0
High-grade stenosis; differentiate from near occlusion.
80–89%
no own cutoff
>140
no own cutoff
Very high diastolic velocity supports high grade.
>90%
>400
no own cutoff
>5,0
Velocity may paradoxically fall if near occlusion is present.
Near occlusion
variable — threadlike flow
variable
variable
Diagnosis is morphologic/color Doppler-based; it does not depend on a fixed cutoff.
Occlusion
absence of flow
absence of flow
not applicable
No detectable patent lumen.
Use the NASCET method for the reported percentage. Systolic velocity is the primary criterion; diastolic velocity and ratios confirm when velocity is affected by hemodynamic factors.
Source: DIC/SBC + CBR + SBACV 2023
IAC 2023 — modified internal carotid criteria
Category
Internal systolic velocity
Plaque estimate
Internal/common systolic ratio
Internal diastolic velocity
Normal
<180
none
<2,0
<40
<50%
<180
<50%
<2,0
<40
50–69%
180–230
>50%
2,0–4,0
40–100
>70% up to before near occlusion
>230
>50%
>4,0
>100
Near occlusion
high, low or undetectable
visible
variable
variable
Total occlusion
undetectable
visible, no detectable lumen
not applicable
not applicable
IAC recognizes that 125–180 cm/s with ratio ≥2.0, significant plaque and post-stenotic turbulence may also be 50–69%.
Source: IAC Vascular Testing Communication 2023
SRU 2003 — classic criterion still found in services
Category
Internal systolic velocity
Internal diastolic velocity
Internal/common systolic ratio
Normal
<125
<40
<2,0
<50%
<125
<40
<2,0
50–69%
125–230
40–100
2,0–4,0
70% or more up to near occlusion
>230
>100
>4,0
Near occlusion
variable
variable
variable
Occlusion
no flow
no flow
not applicable
Kept for historical comparison; when used, state the standard adopted by the service.
Source: SRU Consensus Conference 2003
Plaque morphology and surface
Item
Finding
Color reading
No plaque
No focal protrusion and no focal thickening >1.5 mm.
Green if velocities are normal.
Echogenic or calcified plaque
Type III–V; calcification may cast shadow and limit measurement.
Yellow if no stenosis ≥50%; red if it limits assessment or accompanies stenosis.
Predominantly echolucent plaque
Type I–II; associated with greater vulnerability in several classifications.
Red for morphologic risk.
Irregular surface
Irregularity 0.4 to 2.0 mm deep.
Yellow; describe in the report.
Ulceration
Concavity/extension >2.0 mm by the de Bray criterion.
Red; high morphologic risk.
Plaque-RADS 2024 reinforces that plaque morphology/composition complements stenosis percentage, but does not yet replace hemodynamic grading.
Source: DIC/SBC-CBR-SBACV 2023 / Plaque-RADS 2024
Technical checklist — carotid and vertebral arteries
Step
Record
Reason
Longitudinal B-mode
Intima-media thickness when indicated and plaque at bulb/bifurcation.
Defines plaque and anatomic limitations.
Color or power Doppler
Bulb, bifurcation, internal and external carotid arteries.
Locates turbulence, near occlusion and residual flow.
Spectral Doppler
Common carotid systolic velocity; internal carotid systolic and diastolic velocities.
Allows ratio and NASCET grading.
Doppler angle
Correct and keep at or below 60 degrees.
Above this, velocity loses reliability.
Vertebral arteries
Flow direction, spectral pattern and asymmetry; no universal numeric cutoffs in the Brazilian document.
Assessment is qualitative and contextual.
Avoid abbreviations in teaching text: write internal carotid, common carotid, systolic velocity, diastolic velocity and internal/common ratio.