Peripheral Arterial Ultrasound in PAD: AIUM 2025 Protocol
Clinical Objective of the Study
The revision of the AIUM Practice Parameter for the Performance of Peripheral Arterial Ultrasound Using Color and Spectral Doppler, 2025 describes the standard for performing peripheral arterial ultrasound with color and spectral Doppler. For the request of 'intermittent claudication,' the study aims to localize hemodynamically significant stenosis or occlusion, assess the extent of the lesion, and provide a reproducible protocol for a vascular surgeon or angiologist.
Ultrasound Doppler studies are not limited to finding the maximum velocity. The AIUM document emphasizes a comprehensive assessment: B-mode, color Doppler, spectral Doppler, waveform analysis, velocities, and post-stenotic changes. The protocol should document not only 'stenosis presence' but also its location, how it alters blood flow, and which segments are patent distally.
Indications for Suspected PAD
In a vascular laboratory, typical clinical indications include pain on walking, decreased or asymmetric pulse, abnormal results of non-invasive hemodynamic tests, ischemic changes in the foot, and monitoring of previously identified lesions or interventions. In intermittent claudication, the study should address practical questions: iliac-femoral or femoral-popliteal level, whether there is involvement of the leg arteries, and whether there is sufficient data for planning revascularization.
If symptoms do not match findings at the thigh and leg level, more proximal inflow should be considered. In such situations, the common femoral artery is evaluated as an 'inflow window': a monophasic, dampened waveform in the common femoral artery suggests iliac involvement, even if local femoral segment stenosis is not pronounced.
Minimum Protocol for Lower Extremity
The protocol follows the arterial pathway. In the standard logic for the lower extremity, the common femoral artery, bifurcation, deep femoral artery at the origin, superficial femoral artery in proximal, mid, and distal segments, popliteal artery, and then leg arteries are documented according to the clinical task and visualization availability.
In each significant segment, grayscale imaging, a color map of the lumen, and a spectral curve are needed. In cases of focal acceleration, PSV is recorded at the zone of maximum acceleration and in the nearest proximal normal segment to calculate the velocity ratio. In suspected occlusion, the absence of color filling and spectral signal is documented with optimized settings, as well as the site of distal flow restoration if visualized.
Color Doppler Settings
Color Doppler is used as a lumen map and navigator for spectral measurement. Gain, velocity scale, wall filter, and color window angle are optimized to avoid both false absence of flow and color 'overflow' beyond the vessel. Focal aliasing pattern, color mosaic, narrowing of the color channel, and turbulence help locate the site for spectral measurement.
In cases of significant calcification, the color signal may be shielded. In such segments, combining several acoustic windows is useful, and absence of color should not be interpreted as occlusion without spectral verification. For leg arteries, it is especially important not to set the wall filter too high or the scale too high, otherwise low-velocity distal flow will be lost.
Spectral Doppler: Measurement Technique
PSV is measured in the longitudinal plane, with the cursor aligned parallel to the flow direction. According to AIUM, for accurate velocity measurement, the insonation angle should be ≤60°. In tortuous vessels, the angle is aligned with the actual flow direction in the lumen, not with the wall at the adjacent segment.
The sample volume is placed at the zone of maximum velocity, usually at the center of the color acceleration. For the PSV ratio, the velocity in the stenosis and the velocity in the nearest proximal segment without visible local lesion are taken. If the proximal segment is already diffusely altered, the velocity ratio becomes less reliable; then the waveform shape, color signs, and comparison with adjacent levels gain importance.
Stenosis Criteria for Native Peripheral Arteries
AIUM provides Doppler criteria as a basis for a standardized protocol, while the laboratory should apply validated local criteria and consider the clinical context. For native peripheral arteries, the key parameter is the PSV ratio in the stenosis to the PSV in the proximal segment.
| Degree of Diameter Narrowing | PSV Ratio: Stenosis / Proximal Segment | Practical Interpretation |
|---|---|---|
| 0–19% | <1.5 | No hemodynamically significant acceleration |
| 20–49% | 1.5–2.0 | Non-hemodynamically significant stenosis |
| 50–74% | 2.0–4.0 | Hemodynamically significant stenosis |
| 75–99% | >4.0 | High-grade stenosis |
| Occlusion | Color and spectral signal not detected | Extent and distal flow restoration should be indicated |
These categories should not be used mechanically in cases of stents, grafts, significant diffuse lesions, or markedly reduced cardiac output without considering the overall picture. The report should ideally indicate both the category and the actual PSV/PSV ratio to ensure the study is verifiable.
Waveform Analysis
Waveform analysis helps distinguish local stenosis from proximal or distal influence. In a normal peripheral artery of the limb, a high-resistance multiphasic profile is expected. In significant stenosis, focal acceleration, spectral broadening, and turbulence appear at the narrowing; distally, there is reduced pulsatility, delayed systolic rise, and monophasic low-amplitude flow.
For intermittent claudication, segmental logic is important. A monophasic waveform already in the common femoral artery indicates proximal inflow involvement. A normal common femoral waveform with local acceleration in the superficial femoral artery supports the diagnosis of femoral-popliteal stenosis. In occlusion of the superficial femoral artery, collateral restoration is often visualized in the popliteal or distal segment; this should be reflected in the conclusion.
What Must Be Documented
The report should include the side of the study, segments examined, technical limitations, presence of plaques or calcification, artery patency, localization of stenoses and occlusions, PSV at key points, PSV ratio for stenosis, waveform shape proximal and distal to the lesion. For the clinician, the level of the most proximal significant lesion, the extent of occlusion, and the condition of outflow pathways are particularly important.
Formulations are better made anatomically: '50–74% stenosis of the proximal superficial femoral artery with a PSV ratio of 2.8' is more informative than 'flow acceleration in the thigh.' If the study is incomplete due to wound, dressing, gas, obesity, or calcification, this should be noted separately to avoid creating a false impression of complete negative visualization.
Common Errors in Vascular Laboratory
- Measuring PSV at an angle greater than 60° or without aligning the cursor with the flow direction.
- Diagnosing occlusion solely based on absence of color without optimizing the scale and spectral verification.
- Using absolute PSV without reference to the proximal segment.
- Omitting the common femoral artery in symptoms suggestive of iliac involvement.
- Failing to include distal runoff in the conclusion for proximal occlusion.
Practical Report Template
Optimal conclusion: 'The arteries of the right lower extremity were examined from the common femoral to the leg arteries. The waveform in the common femoral artery is multiphasic. In the proximal superficial femoral artery, there is a plaque with local color aliasing; PSV in stenosis …, proximally …, PSV ratio …, corresponding to category … according to AIUM criteria. Distally, the flow … . The popliteal artery and leg arteries … . Conclusion: …'
This protocol links the clinical claudication with the anatomical level of the lesion and maintains the verifiability of each conclusion: the segment is visible, velocity measured, ratio calculated, waveform described.
Frequently asked questions
Is it necessary to always examine the leg arteries in claudication?
Yes, if the goal is to assess patency and outflow for clinical decision-making. At a minimum, available distal segments should be documented, and limitations should be noted if the leg arteries are not fully evaluated.
Why is the PSV ratio more important in the protocol than just the maximum velocity?
The PSV ratio compares acceleration in the stenosis with the nearest proximal segment and better reflects local hemodynamic significance, especially with differences in systemic pressure and overall blood flow.
How to interpret the absence of color signal in a calcified artery?
The absence of color alone does not equal occlusion. Settings should be optimized, alternative windows sought, and the absence of flow confirmed with spectral Doppler; technical limitations should be noted in the report.