Duplex Ultrasound is the Recommended Initial Diagnostic Test for Arterial Evaluation
Duplex ultrasound (DUS) is recommended as the first-line non-invasive test for evaluating blood flow and identifying stenosis or occlusion in affected arteries. 1
What is Duplex Ultrasound?
Duplex ultrasound combines two imaging modalities:
- 2-dimensional real-time imaging (B-mode)
- Doppler flow analysis
This combination allows for:
- Direct visualization of vessel anatomy
- Measurement of blood flow velocity
- Assessment of hemodynamic significance of stenosis
How Duplex Ultrasound Works for Arterial Assessment
DUS does not directly measure the diameter of the artery or stenotic lesion. Instead, it uses blood flow velocity as an indicator of stenosis severity 1. The key parameters measured include:
- Peak systolic velocity (PSV) at the stenotic segment
- End diastolic velocity (EDV)
- Velocity ratios between stenotic segments and adjacent normal segments
- Spectral waveform analysis
Diagnostic Accuracy
DUS demonstrates excellent diagnostic accuracy:
- Sensitivity and specificity >90-95% for detecting stenoses >50% in diameter from the iliac arteries to the popliteal arteries 1
- High correlation with angiographically determined arterial stenosis 1, 2
Advantages of Duplex Ultrasound
- Non-invasive with no radiation exposure
- Widely available and relatively inexpensive
- Real-time imaging allows dynamic assessment
- Can be performed at bedside
- Provides both anatomical and functional information
- No contrast agents required
- Can be repeated safely for follow-up
Interpretation of Arterial Stenosis by DUS
For carotid artery stenosis, velocity criteria typically define two categories 1:
50% to 69% stenosis:
- Visible plaque
- PSV of 125 to 230 cm/s in the internal carotid artery
- Internal/common carotid artery PSV ratio between 2 and 4
- EDV of 40 to 100 cm/s
70% to 99% stenosis:
- PSV >230 cm/s
- Internal/common carotid artery PSV ratio >4
- EDV >100 cm/s
For superficial femoral artery stenosis 3:
- 50%-69% stenosis: PSV ≥210 cm/s
- 70%-99% stenosis: PSV ≥275 cm/s or PSV ratio ≥4.0
Limitations and Pitfalls
- Operator-dependent technique requiring skilled technologists
- May have difficulty with:
- Heavily calcified vessels
- Distinguishing subtotal from complete occlusion
- Multiple sequential lesions
- Deep vessels (e.g., iliac arteries)
- Bowel gas interference
- Velocity criteria may vary between laboratories, requiring local validation
When to Consider Additional Imaging
Additional imaging modalities should be considered when:
- DUS results are equivocal or technically limited
- Planning endovascular intervention (to assess vessel anatomy)
- Discrepancy exists between clinical presentation and DUS findings
- Need to evaluate arterial segments not accessible by ultrasound
Options include:
- CT angiography (CTA)
- MR angiography (MRA)
- Digital subtraction angiography (DSA) - reserved for cases requiring intervention or when non-invasive imaging is inconclusive
Guideline Recommendations
The American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines strongly recommends 1:
"In asymptomatic patients with known or suspected carotid stenosis, duplex ultrasonography, performed by a qualified technologist in a certified laboratory, is recommended as the initial diagnostic test to detect hemodynamically significant carotid stenosis." (Class I, Level of Evidence: C)
"It is reasonable to perform duplex ultrasonography to detect hemodynamically significant carotid stenosis in asymptomatic patients with carotid bruit." (Class IIa, Level of Evidence: C)
The European Society of Cardiology (ESC) guidelines state 1:
- "DUS is indicated as a first-line imaging method to confirm LEAD lesions." (Class I, Level of Evidence: C)
In summary, duplex ultrasound should be the initial diagnostic test for evaluating arterial blood flow and identifying stenosis or occlusion, with additional imaging modalities reserved for specific scenarios requiring more detailed anatomical information or when DUS results are inconclusive.