From the Guidelines
To interpret an arterial duplex ultrasound, systematically evaluate blood flow in arteries using both B-mode imaging and Doppler waveform analysis, focusing on vessel anatomy, blood flow characteristics, and velocity measurements to determine the presence, location, and severity of arterial disease. When interpreting the results, consider the sensitivity and specificity of duplex ultrasound for diagnosing stenoses >50% in diameter, which are approximately 90% to 95% from the iliac arteries to the popliteal arteries 1. The accuracy of duplex ultrasound depends on the ability to visualize the vessel adequately, and the use of color Doppler improves accuracy 1.
Key steps in interpretation include:
- Identifying vessel anatomy on grayscale imaging, noting vessel wall thickness, presence of plaque, and any stenosis or occlusion
- Assessing blood flow characteristics using color Doppler to visualize flow direction and areas of turbulence
- Measuring peak systolic velocity (PSV) and end-diastolic velocity (EDV) at multiple locations, particularly before, at, and after suspected stenotic areas
- Calculating velocity ratios between stenotic segments and adjacent normal segments; a ratio exceeding 2:1 typically indicates hemodynamically significant stenosis
- Paying attention to waveform morphology distal to stenosis, which often shows dampening with decreased amplitude and loss of reverse flow component
- Identifying collateral pathways in cases of occlusion
According to the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, duplex ultrasound is useful for diagnosing anatomic location and degree of stenosis of peripheral artery disease (PAD) and is recommended for routine surveillance after femoral-popliteal or femoral-tibial-pedal bypass with a venous conduit 2. However, it is essential to consider the limitations of duplex ultrasound, including limited sonographic windows and potential underestimation of the extent of disease when multiple "tandem" stenotic segments are present in series 1.
In clinical practice, duplex ultrasound should be used as a first-line imaging modality for patients with suspected PAD, given its portability, lack of IV contrast agent, and ability to provide valuable information on blood flow and vessel anatomy. However, in cases where duplex ultrasound is inconclusive or inadequate, other imaging modalities such as computed tomography angiography (CTA) or magnetic resonance angiography (MRA) may be necessary to provide a more comprehensive evaluation of the arterial disease 1.
From the Research
Interpreting Arterial Duplex Ultrasound
To interpret an arterial duplex ultrasound, it is essential to understand the components of the test and the information it provides.
- Duplex ultrasound combines B-mode imaging and pulsed Doppler flow analysis to evaluate atherosclerotic arterial disease 3.
- The test provides information about the degree of stenosis, location of disease, and plaque characterization 3.
- It is used to detect renal artery stenosis, mesenteric artery stenosis, peripheral vascular disease, and venous disease 3.
Components of Arterial Duplex Ultrasound
The test includes:
- B-mode imaging: provides images of the arterial structure
- Pulsed Doppler flow analysis: measures blood flow through the arteries
- Color flow Doppler: allows for the visualization of blood flow in the arteries 3
Accuracy and Limitations
- Duplex ultrasound is accurate in detecting arterial stenosis and occlusion, with an accuracy that rivals angiography 3.
- However, its accuracy may be affected by multisegmental disease, with lower sensitivity for detecting significant stenoses distal to severe or total occlusions 4.
- New developments in power Doppler imaging and ultrasound contrast agents may improve the accuracy of duplex ultrasound 4.
Comparison with Other Imaging Modalities
- Duplex ultrasound has been compared to CT angiography in several studies, with varying results:
- In the iliac arterial district, CT angiography was found to be more accurate than duplex ultrasound 5, 6.
- In the femoro-popliteal district, duplex ultrasound was found to have good diagnostic concordance with CT angiography 5, 6.
- In the infra-geniculate area, CT angiography was found to have a lower accuracy than duplex ultrasound 5, 6.