Carotid Ultrasound Normal Values: IMT, PSV, and Stenosis Criteria

Carotid ultrasound is one of the most technically demanding and clinically significant exams in vascular sonography. The velocities you record and the stenosis grade you assign directly influence whether a patient gets medical management or surgical intervention. Accuracy is non-negotiable.

This guide covers the carotid ultrasound normal values you need — IMT, PSV, end-diastolic velocities, and the SRU 2003 stenosis criteria applied correctly.

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Carotid Anatomy Review

The carotid duplex examination evaluates bilateral carotid and vertebral arteries:

• Common carotid artery (CCA) — from the clavicular level to the bifurcation
• Internal carotid artery (ICA) — branches from the bifurcation, supplies the brain
• External carotid artery (ECA) — branches from the bifurcation, supplies the face
• Vertebral arteries — travel in the foramina transversaria of the cervical vertebrae

The ICA is the clinically critical vessel. ECA disease is generally less relevant for stroke risk.

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Normal Carotid Velocities

Common Carotid Artery (CCA)

Parameter	Normal Value
PSV	60 – 100 cm/s
EDV	15 – 30 cm/s
Waveform character	Low-resistance (continuous forward diastolic flow)

Internal Carotid Artery (ICA)

Parameter	Normal Value
PSV	< 125 cm/s
ICA/CCA PSV ratio	< 2.0
Waveform character	Low-resistance (similar to CCA)

External Carotid Artery (ECA)

Parameter	Normal Value
PSV	40 – 80 cm/s
Waveform character	High-resistance (triphasic or bidirectional)

Distinguishing ICA from ECA: The ECA has temporal artery tap response (velocity oscillations when the temporal artery is tapped), and a higher-resistance waveform. The ICA is larger at origin, has no branches in the neck, and has a low-resistance waveform.

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SRU 2003 Carotid Stenosis Criteria

The Society of Radiologists in Ultrasound (SRU) 2003 consensus is the standard for ICA stenosis grading in the United States.

Stenosis Grade	ICA PSV	ICA/CCA PSV Ratio	ICA EDV
Normal / < 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	—	—

Why All Three Parameters Matter

• ICA PSV alone can be falsely elevated in patients with high cardiac output (anemia, fever, hyperthyroidism, young age)
• ICA/CCA ratio corrects for cardiac output by normalizing to the same patient's CCA velocity
• ICA EDV > 100 cm/s confirms high-grade stenosis when PSV and ratio are borderline

Always use all three parameters together. A patient with ICA PSV 240 cm/s but ICA/CCA ratio 3.8 and EDV 90 cm/s deserves caution about calling ≥ 70%.

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The Near-Occlusion Pitfall

Near-occlusion (> 90–99% stenosis) can paradoxically show lower velocities than a 70–79% stenosis because the residual lumen is so narrow that flow becomes severely reduced.

Classic appearance of near-occlusion:

• Thread-like color flow in the ICA on color Doppler
• "String sign" on power Doppler
• Low or variable velocities — do not exclude from ≥ 70% grading
• Ipsilateral CCA may also show reduced flow

If the vessel appears severely narrowed on grayscale but the PSV seems low for the appearance, consider near-occlusion rather than normal. Communication with the interpreting radiologist is appropriate.

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Contralateral Disease Effect

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 PSV.

Always:

1. Evaluate both sides before interpreting velocities
2. Note any contralateral disease in the report
3. Adjust interpretation accordingly ("elevated velocities in the setting of contralateral occlusion may not represent ipsilateral stenosis")

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Intima-Media Thickness (IMT)

IMT is a measurement of atherosclerotic burden and cardiovascular risk, distinct from stenosis grading.

Measurement

• Location: CCA posterior wall, 1 cm proximal to the bifurcation
• Plane: Longitudinal; the intima and media appear as two echogenic lines with a hypoechoic layer between
• Method: Distance from leading edge of intimal-lumen interface to media-adventitia interface

Normal IMT Values (Adult)

Age Group	Normal CCA IMT
< 40 years	< 0.6 mm
40–60 years	< 0.8 mm
> 60 years	< 1.0 mm

IMT > 1.0 mm anywhere in the carotid system is generally considered thickened. IMT measurement has largely fallen out of routine clinical use for individual patient management but remains in research protocols.

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Vertebral Artery Assessment

Parameter	Normal Finding
Flow direction	Antegrade (toward brain = cephalad)
Waveform	Low-resistance, similar to ICA
Symmetry	Flow may be asymmetric (dominant side)

Vertebral Artery Steal

When subclavian artery stenosis is proximal to the vertebral artery origin, the vertebral artery acts as a collateral — flow reverses (caudal instead of cephalad). This is subclavian steal syndrome.

Document:

• Antegrade flow (normal)
• Retrograde flow (complete steal)
• To-and-fro / alternating flow (partial steal — confirm with arm hyperemia maneuver)

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Plaque Characterization

When plaque is identified, document:

Feature	What to Note
Location	CCA, bulb, proximal ICA/ECA
Length	Longitudinal extent in cm
Echogenicity	Echogenic (fibrous/calcified) vs. hypoechoic (lipid-rich — higher embolic risk)
Surface	Smooth vs. irregular vs. ulcerated
Calcification	Present/absent; shadowing noted

Heterogeneous/hypoechoic plaque is associated with higher stroke risk than homogeneous/echogenic plaque, even at the same stenosis grade.

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Key Images for Your Worksheet

1. CCA — longitudinal, bilateral with PSV spectral Doppler
2. CCA — grayscale, bilateral (IMT if requested)
3. Carotid bifurcation — longitudinal and transverse (grayscale)
4. ICA — longitudinal, bilateral with PSV, EDV spectral Doppler
5. ICA/CCA ratio — documented on worksheet
6. ECA — bilateral with spectral Doppler (confirm temporal tap)
7. Vertebral arteries — bilateral with flow direction confirmed
8. Color Doppler — bilateral carotids at bifurcation
9. Any plaque — three-plane views with characterization

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Quick Reference: SRU 2003 at a Glance

Grade	ICA PSV	Ratio	EDV
Normal	< 125	< 2.0	—
50–69%	125–230	2.0–4.0	—
≥ 70%	> 230	> 4.0	> 100
Near-occlusion	Variable	Variable	Variable
Occlusion	No flow	—	—

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Use the SonoBuddy Carotid Calculator

SonoBuddy's Carotid Stenosis Calculator takes your ICA PSV, ICA EDV, and CCA PSV, calculates the ICA/CCA ratio automatically, and returns the stenosis grade per SRU 2003 criteria with color-coded severity.

Open SonoBuddy → Calculators → Carotid Stenosis.

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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. Clinical decisions must involve the ordering provider and interpreting physician.