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ULTRASOUND
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Carotid Doppler Ultrasound

Carotid duplex ultrasound combines B-mode imaging with color and spectral Doppler to evaluate the extracranial carotid and vertebral arteries for atherosclerotic disease. It quantifies internal carotid artery stenosis using velocity criteria and characterizes plaque, guiding decisions on carotid endarterectomy or stenting. It is the first-line, noninvasive test in the workup of stroke, TIA, and asymptomatic bruit.

Indications

  • Recent stroke, transient ischemic attack, or amaurosis fugax
  • Asymptomatic cervical bruit
  • Screening in patients with significant atherosclerotic risk factors or before major cardiovascular surgery
  • Surveillance following carotid endarterectomy or stenting
  • Follow-up of known carotid stenosis
  • Evaluation of pulsatile neck mass or suspected carotid dissection
  • Assessment of subclavian steal with vertebral artery flow direction

Contraindications & Cautions

  • No contraindications; noninvasive and radiation-free
  • Extensive vessel calcification causes acoustic shadowing and can preclude accurate velocity measurement
  • High carotid bifurcation or short thick neck may limit access
  • Not reliable for intracranial or ostial great-vessel disease; CTA or MRA may be needed
  • Follow ALARA for Doppler exposure

Patient Preparation

  • No fasting or specific preparation required
  • Supine positioning with the head slightly extended and turned away from the side being examined
  • Remove neck jewelry and high collars
  • No consent required for diagnostic scanning
  • Document blood pressure and relevant symptoms and laterality

Technique & Parameters

  • High-frequency linear transducer (5-7 MHz); lower frequency for deep or large necks
  • Grayscale survey of common, internal, and external carotid arteries and vertebral arteries in transverse and longitudinal planes
  • Characterize plaque location, extent, surface, and echogenicity
  • Color Doppler to identify flow, turbulence, and areas of aliasing
  • Spectral Doppler with angle correction at 60 degrees or less measuring peak systolic velocity (PSV) and end-diastolic velocity (EDV) in the CCA, ICA, and ECA
  • Calculate ICA/CCA PSV ratio
  • Determine vertebral artery flow direction (antegrade versus retrograde)
  • Apply the Society of Radiologists in Ultrasound consensus velocity criteria

Systematic Review

  • Common carotid artery: intima-media thickness, plaque, velocities
  • Carotid bulb and bifurcation: plaque burden and surface characteristics
  • Internal carotid artery: PSV, EDV, spectral broadening, degree of stenosis
  • External carotid artery: identify by branches and temporal tap to distinguish from ICA
  • ICA/CCA PSV ratio
  • Vertebral arteries: presence, direction of flow, and velocities
  • Plaque morphology: calcified, echolucent, ulcerated, heterogeneous
  • Post-intervention: stent patency, in-stent velocities, endarterectomy site

Key Findings & Significance

  • ICA PSV <125 cm/s with no plaque indicates normal or <50% stenosis
  • ICA PSV 125-230 cm/s indicates 50-69% stenosis
  • ICA PSV >230 cm/s with EDV >100 cm/s and ICA/CCA ratio >4 indicates 70-99% stenosis
  • Absence of flow with a visible lumen thrombus indicates occlusion
  • String sign of trickle flow indicates near-occlusion
  • Retrograde vertebral flow indicates subclavian steal
  • Echolucent, irregular, or ulcerated plaque carries higher embolic risk

Differential Considerations

  • Elevated ICA velocity: true stenosis, tortuosity, contralateral occlusion causing compensatory flow, or post-stenotic hyperemia
  • Absent ICA flow: occlusion versus near-occlusion versus technical artifact from calcification
  • Low CCA velocities: proximal common carotid or innominate stenosis, cardiac dysfunction, aortic stenosis
  • Pulsatile neck mass: tortuous carotid, aneurysm, carotid body tumor, dissection
  • Retrograde vertebral flow: subclavian steal from proximal subclavian stenosis
  • Elevated velocities post-stenting: in-stent restenosis versus normal stent-related velocity elevation

Pearls & Pitfalls

  • Distinguish ICA from ECA using branch pattern, waveform, and the temporal tap maneuver
  • Contralateral high-grade stenosis or occlusion elevates ipsilateral ICA velocities and can cause overestimation
  • Heavy calcification shadows the vessel; report velocities as limited and consider CTA/MRA
  • Maintain a Doppler angle of 60 degrees or less to keep velocity measurements accurate
  • Near-occlusion may show paradoxically low velocities; grayscale and color confirm the trickle of flow
  • Report plaque morphology, as ulcerated or echolucent plaque is clinically relevant beyond stenosis grade
  • Post-endarterectomy and post-stent studies use different velocity thresholds

Structured Report

  • State indication and symptomatic laterality
  • Report plaque location, extent, and morphology bilaterally
  • Report PSV and EDV for CCA, ICA, and ECA, and the ICA/CCA ratio
  • State the degree of stenosis category for each ICA per consensus criteria
  • Report vertebral artery flow direction and any subclavian steal
  • Note technical limitations such as calcification
  • Impression: degree of stenosis per side with recommendation for surgical/endovascular referral or surveillance interval

References

  • Grant EG et al. Carotid Artery Stenosis: Grayscale and Doppler Ultrasound Diagnosis - Society of Radiologists in Ultrasound Consensus Conference
  • NASCET (North American Symptomatic Carotid Endarterectomy Trial) stenosis measurement
  • ACR-AIUM-SRU Practice Parameter for the Performance of an Ultrasound Examination of the Extracranial Cerebrovascular System
  • ACR Appropriateness Criteria: Cerebrovascular Disease

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.