Carotid stenosis — US / CTA (NASCET)

USCTSRU 2003 / NASCET

Grading of internal carotid artery stenosis on Doppler ultrasound or CTA.

Applies to

Suspected carotid stenosis on Doppler US or CTA/MRA

Does not apply to

Post-endarterectomy or post-stent surveillance (velocity criteria differ)
Near-occlusion, where velocity criteria break down

What to report

Tap an item to check it off while dictating.

1.Velocities
ICA and CCA peak systolic (PSV) and end-diastolic (EDV) velocities on ultrasound.
2.ICA/CCA ratio
PSV ratio corroborates the PSV-based category, especially with tandem disease or contralateral occlusion.
3.Plaque morphology
Calcified, soft/echolucent, or ulcerated; extent and surface.
4.NASCET measurement (CTA)
Narrowest residual lumen against the normal distal ICA; report percent stenosis.
Pitfall: Measure the distal ICA where walls are parallel and normal — not within the bulb.
5.Tandem and vertebral disease
Proximal/distal tandem lesions and vertebral flow (including subclavian steal).

Scores & calculators

Carotid US velocity criteria

SRU consensus 2003

Doppler estimate of ICA stenosis from peak systolic velocity.

ICA peak systolic velocity (PSV)

Complete the inputs to see the result.

NASCET carotid stenosis

Percent internal carotid stenosis by the NASCET method (from CTA/MRA/DSA).

Residual (narrowest) lumen

Normal distal ICA lumen

Complete the inputs to see the result.

NASCET % = (1 − narrowest ICA lumen / normal distal ICA lumen) × 100. In near-occlusion the distal ICA collapses, invalidating the ratio — report as 'near-occlusion' rather than a percentage.

Sources

Carotid US consensus — Grant EG et al. Radiology (SRU) (2003)
NASCET — North American Symptomatic Carotid Endarterectomy Trial. NEJM (1991)

Content review: Content pending clinical review · 2026-07-09

Educational reference for trained clinicians. Verify every result against the cited original guideline before use. Not a substitute for clinical judgment or medical advice.