Indications
Screening and follow-up of carotid atherosclerotic disease (cardiovascular risk factors, carotid bruit, previous TIA or stroke), preoperative assessment (cardiac surgery, carotid surgery), surveillance after endarterectomy or stenting, suspected dissection, suspected subclavian steal syndrome, and assessment of the vertebral arteries in vertebrobasilar symptoms.
Equipment
- Linear array transducer, high frequency, 7–12 MHz: at the depth of the neck vessels (2–4 cm) a lower frequency is unnecessary and counterproductive.
- Vascular or carotid preset, with colour gain and PRF adjusted to avoid both aliasing and under-representation of low-velocity flow.
- Doppler pulsato con angolo di insonazione ≤ 60°, idealmente 45–60°, mantenuto costante nei controlli seriati per rendere confrontabili le velocità nel tempo.
- A narrow sample volume (1.5–2 mm), placed in the centre of the lumen and moved along the whole suspect segment so that the point of peak velocity is not missed.
Patient position
Patient supine, head slightly extended on a thin pillow and rotated about 30–45° away from the side being examined. The operator may sit at the head of the couch or beside the patient, according to personal preference; both approaches are valid provided they are systematic and reproducible.
Systematic scanning
The sequence should always be carried out on both sides, in longitudinal and transverse planes, combining B-mode, colour Doppler and pulsed-wave Doppler.
4.1 · Common carotid artery (CCA)
Begin in the transverse plane at the base of the neck and move up to the bifurcation, to gain an overall impression of calibre and patency. Then switch to the longitudinal plane: assess the intima-media thickness (IMT) on the posterior wall, 1–2 cm proximal to the bulb, in a straight plaque-free segment — this is where the measurement is most reproducible.
4.2 · Carotid bulb
The commonest site of plaque: assess it with multiple views (anterolateral, lateral, posterolateral), because an eccentric plaque can be missed from a single angle. Colour Doppler here normally shows an area of reversed flow along the outer wall of the bulb (flow separation), which should not be mistaken for pathological turbulence.
4.3 · Internal carotid artery (ICA)
Follow the vessel distally as far as the acoustic window allows (often limited by the angle of the mandible). Sample with pulsed-wave Doppler just beyond the bulb, where velocities are most representative, and along the whole accessible segment if plaque is present, looking for the point of maximum systolic acceleration.
4.4 · External carotid artery (ECA)
Course più anteriore e mediale, con le prime collaterali visibili poco dopo l'origine (tiroidea superiore, in genere il primo ramo identificabile). Utile per la diagnosi differenziale con l'ICA (vedi sezione 5).
Distinguishing ICA from ECA
Misidentification invalidates the entire assessment of the degree of stenosis. No single sign is conclusive on its own: several criteria should be combined.
| Criterion | ICA | ECA |
|---|---|---|
| Branches | None in the cervical segment | Present (superior thyroid, facial, etc.) |
| Course | Typically posterolateral | Typically anteromedial |
| Baseline calibre | Usually larger | Usually smaller |
| Flow profile | Low resistance (diastolic flow always present, even without stenosis) | High resistance (little or no diastolic component) |
| Temporal tap test | No transmitted oscillation | Oscillations transmitted to the Doppler trace when tapping the ipsilateral superficial temporal artery |
Vertebral arteries and subclavian steal
These are assessed in their extracranial course (V2), seen in a paramedian longitudinal view between the cervical transverse processes, recognisable by the regular "stepladder" acoustic shadowing of the processes themselves. Document calibre, flow direction and symmetry with the contralateral side.
Where subclavian steal syndrome is suspected (blood pressure asymmetry between the arms, upper limb claudication, vertebrobasilar symptoms), the vertebral artery is assessed at rest and then during reactive hyperaemia: a sphygmomanometer cuff on the ipsilateral arm is inflated above systolic pressure for 2–3 minutes and then released abruptly while the vertebral artery is observed — flow that transiently reverses, or becomes more markedly retrograde, confirms haemodynamically significant steal.
What to measure and document
- IMT in mm, on the posterior wall of the distal CCA, in a plaque-free segment.
- Plaque: site, structure (calcific, soft/hypoechoic, mixed), surface (smooth or irregular) and extent.
- ICA PSV and EDV at the point of maximum stenosis, with angle correction: these are the key parameters for grading (see the guidelines for thresholds).
- CCA PSV, for the ICA/CCA velocity ratio, which is useful when a systemic hyperdynamic state raises absolute velocities uniformly.
- Flow direction in the vertebral arteries and, where relevant, the result of the reactive hyperaemia manoeuvre.