Synopsis
Use B-mode, colour and spectral Doppler findings as one coherent haemodynamic examination, grade carotid and limb arterial disease without over-reading a single number, and know when ultrasound should guide urgent referral rather than delay definitive vascular or stroke care.
- Duplex combines anatomy from B-mode, flow direction and distribution from colour, and velocity plus waveform shape from spectral Doppler.
- Doppler velocity depends on insonation angle; keep the angle correction cursor parallel to the vessel or flow jet and use the laboratory's validated angle convention.
- For stable suspected lower-limb peripheral arterial disease, examine pulses and measure ankle-brachial pressure index first, then use duplex as first-line anatomical imaging when revascularisation is being considered.
Key red flags
Current focal neurological deficit, cortical signs or reduced consciousness: activate the acute stroke pathway rather than booking routine carotid ultrasound.
A recent resolved focal neurological event compatible with TIA: arrange immediate specialist assessment within 24 hours; urgent carotid imaging is required if carotid endarterectomy may be appropriate.
Sudden limb pain with pallor, pulselessness, paraesthesia, weakness or coldness: suspect acute limb ischaemia and obtain emergency vascular input.
Rapidly expanding or pulsatile mass, active bleeding after vascular access, or duplex evidence of pseudoaneurysm with threatened skin or distal perfusion: seek urgent vascular review.
A technically limited scan that does not explain a high-risk presentation is uncertainty, not reassurance; escalate to cross-sectional angiography or the acute pathway.
Near-occlusion is severe internal-carotid narrowing with reduced distal calibre or flow. Velocity may be very high at a tight jet, low when flow collapses, or difficult to detect. True occlusion requires careful low-flow colour and spectral settings and demonstration that no patent lumen remains; calcific shadow or an inadequately visualised distal segment should prompt confirmatory imaging when the distinction changes treatment.
Acute arterial occlusion may show intraluminal material and an abrupt flow cutoff, but age cannot always be assigned reliably from echogenicity alone. A pseudoaneurysm typically has swirling bidirectional sac flow and a to-and-fro neck waveform. Symptoms, distal perfusion, recent access and expansion determine urgency; do not compress a suspected pseudoaneurysm before vascular assessment.
Investigation priorities
Identify extracranial carotid plaque, distinguish patency from occlusion and estimate stenosis severity when the result will guide secondary prevention or carotid intervention.
Provide NICE-recommended first-line anatomical imaging when lower-limb revascularisation is being considered, localising and characterising inflow, femoropopliteal and tibial disease.
Management branches
A resolved focal neurological episode is clinically compatible with TIA and carotid endarterectomy could be appropriate.
- Arrange immediate specialist assessment within 24 hours and begin the indicated secondary-prevention pathway; ultrasound is not a substitute for confirming that the event was focal and vascular.
- Obtain urgent carotid imaging through the specialist pathway, usually duplex first where a validated service can provide reliable grading quickly.
Exertional leg discomfort, impaired walking or pulse findings suggest lower-limb peripheral arterial disease without an acutely threatened limb.