Lower-limb arterial duplex — full runoff mapping
Distal aorta and common, internal and external iliac arteries where insonation allows, then common femoral, profunda, superficial femoral, popliteal, and the anterior tibial, posterior tibial and peroneal arteries to the ankle; grafts and stents along their whole length where present.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Intermittent claudication or rest pain, as the first-line imaging test under NICE CG147 once the diagnosis is suspected clinically and by ankle-brachial pressure index.
- Assessment of disease level and pattern before deciding whether revascularisation is realistic — which is the question that then justifies CT or MR angiography.
- Surveillance of infrainguinal bypass grafts and of stented segments.
- Suspected popliteal aneurysm or popliteal entrapment, where duplex can be performed dynamically.
- Patients in whom iodinated contrast or gadolinium is undesirable and an anatomical answer is still needed.
Technique
- Grading rests on spectral waveform shape and on peak systolic velocity ratio across a lesion rather than on absolute velocity, which is why a static image alone is not a report.
- A monophasic or damped waveform distal to a segment localises disease even where the segment itself could not be insonated directly.
- Aortoiliac segments are the least reliably seen, particularly in a gaseous or large abdomen; the report should state which segments were not assessed rather than leaving it implied.
Where it goes wrong
- Heavy calcification causes shadowing and can make a stenosis ungradeable — this is a technical limitation to be declared, and it is the legitimate trigger for CT or MR angiography.
- Duplex under-reads tibial and pedal runoff compared with catheter angiography, so a duplex that shows no distal target should not by itself close the door on revascularisation.
- A normal duplex at rest does not exclude significant disease in a patient with exertional symptoms; exercise testing with post-exercise ankle pressures remains the functional test.
- Velocity thresholds differ between laboratories, so a grade quoted from one department is not directly comparable with another.
Clinical questions that reach this study
Contrast
None
Acquisition
- Preparation
- Supply the ankle-brachial pressure index and the claudication distance or rest-pain history: duplex is graded against the haemodynamic question being asked. Declare previous bypass grafts, stents and amputations — graft surveillance is a different examination from native-vessel mapping.