CardiologyTier 2Topic

Duplex ultrasound scans

Principle

Combines B-mode (greyscale structural) ultrasound with Doppler (flow velocity) imaging - the primary non-invasive vascular imaging modality for arterial and venous disease
Operator-dependent but avoids radiation/contrast, making it first-line for many vascular indications, especially DVT and carotid disease

Applications

Application	Use
Carotid duplex	Stenosis grading (by peak systolic velocity) for stroke/TIA workup and carotid endarterectomy decision-making
Venous duplex	DVT diagnosis - non-compressibility of the vein is the key diagnostic sign
Arterial duplex (limb)	PAD localisation/severity, surveillance of bypass grafts
Renal artery duplex	Renal artery stenosis screening (resistive index, peak velocity)

Interpretation

Velocity criteria (not just visual narrowing) determine stenosis severity grading - e.g. carotid stenosis severity is defined by specific peak systolic velocity thresholds, not diameter reduction alone

Acting on the result

Non-compressibility on venous duplex is diagnostic for DVT without needing venography
Carotid duplex findings directly inform surgical/interventional referral thresholds

Associations

DVT, carotid artery stenosis, peripheral arterial disease, renal artery stenosis

Surveillance

Used serially for graft surveillance after bypass surgery and to monitor known stenosis progression

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