Duplex Ultrasound and Vascular Laboratory Quality

7.1Vascular laboratory protocols and appropriate use

Abbreviations used in this chapter: PSV, peak systolic velocity; EDV, end-diastolic velocity; ICA/CCA ratio, internal-to-common carotid artery peak systolic velocity ratio; ABI, ankle-brachial index; TBI, toe-brachial index; CTA, computed tomography angiography; MRA, magnetic resonance angiography; EVAR, endovascular aneurysm repair; DVT, deep vein thrombosis. In the diagnostic-accuracy discussion, AUC means area under the receiver-operating-characteristic curve, not appropriate-use criteria. VGST is the Vein Graft Surveillance Trial.

Organizations and guidance: IAC, Intersocietal Accreditation Commission; SVU, Society for Vascular Ultrasound; AIUM, American Institute of Ultrasound in Medicine; ACR, American College of Radiology; SRU, Society of Radiologists in Ultrasound; SVS, Society for Vascular Surgery; ESVS, European Society for Vascular Surgery; AHA, American Heart Association; KDOQI, Kidney Disease Outcomes Quality Initiative.

Duplex ultrasound operates as a formal protocol rather than an ad hoc examination, relying on documented minimum professional elements for image acquisition, equipment settings, and quality review SVU Vascular Technology 2019 · SVU Professional Performance Guidelines. Accreditation requires facilities to maintain local operating criteria and structured peer review, creating a governed framework for diagnosis rather than supplying universal disease-specific intervention thresholds IAC Testing Standards. The clinical indication determines the diagnostic pathway, ensuring the protocol accurately targets extracranial, peripheral arterial, or peripheral venous anatomy AIUM Arterial Parameter 2021 · AIUM Venous Parameter 2020.

Appropriateness criteria regulate the initial selection of duplex against cross-sectional or invasive modalities. Multi-society ratings define appropriate use based on whether the examination will change treatment, urgency, or follow-up AUC Peripheral Ultrasound 2012. In practice, imaging selection for chronic lower-extremity claudication, acute limb ischemia, and suspected abdominal aortic aneurysm is driven by scenario-specific appropriateness scores rather than routine reflex ACR Appropriateness 2023 (2 sources) · ACR Appropriateness 2022. Noninvasive arterial testing escalates in a fixed order:

1. Resting ankle-brachial index, adding toe-brachial index where medial calcification is suspected AIUM Arterial Parameter 2021.
2. Segmental pressures with Doppler waveforms or pulse-volume recordings to localise the level of disease AIUM Arterial Parameter 2021.
3. Duplex ultrasound for velocity-based stenosis grading and graft or stent surveillance AIUM Practice Parameter 2022.
4. Cross-sectional imaging (CTA or MRA) or catheter angiography when intervention is planned or duplex is inconclusive ACR Appropriateness 2022.

7.2Carotid duplex criteria and interpretation

Extracranial cerebrovascular interpretation integrates grayscale plaque morphology, color Doppler appearance, spectral waveforms, and velocities into a composite diagnostic grading IAC Standards 2025 · AIUM Practice Parameter 2023 · AIUM Extracranial Parameter 2022. Relying on a single peak systolic velocity (PSV) detached from waveform context and side-to-side comparison introduces critical diagnostic error. The IAC 2023 modified native-carotid criteria use PSV 180–230 cm/s for 50–69% stenosis, interpreted with plaque, ICA/CCA velocity ratio and EDV. PSV 125–180 cm/s can also fit that category when the ratio is at least 2.0 and plaque and other findings support stenosis. Normal arteries have no plaque; plaque-bearing arteries with less than 50% narrowing are a separate category even when velocities are low. PSV above 230 cm/s, ratio above 4.0 and EDV above 100 cm/s support high-grade stenosis below near-occlusion. Diagnostic grade alone does not establish an indication for surgery IAC 2026. Near-occlusion defeats ordinary velocity grading: flow may read high, low, or undetectable, and grayscale and color findings can raise suspicion SRU Consensus 2003. Duplex alone cannot reliably distinguish near-occlusion from conventional high-grade stenosis, particularly without full distal ICA collapse. Suspected or indeterminate cases require confirmatory angiographic imaging with assessment of distal ICA calibre, using CTA or an appropriate MRA technique. Proposed duplex rule-in/rule-out criteria and diameter-based cutoffs require external validation before routine clinical implementation Duplex ultrasound 2026 · Rule-out rule-in 2025 · Near-occlusion is 2021. Subsequent treatment decisions require integration with secondary stroke prevention algorithms and patient symptom status ESVS 2023 · Kleindorfer et al. (2021).

Carotid artery stenting alters local hemodynamics, rendering native-vessel criteria inaccurate. Stented segments require angiography-validated, stent-specific PSV and end-diastolic velocity thresholds to evaluate in-stent restenosis AbuRahma et al. (2008). Laboratory reports must explicitly state whether the evaluated vessel is native or stented to ensure the appropriate criterion set is applied.

7.3Surveillance and venous testing pathways

Post-revascularization duplex establishes interval change through structured comparison with prior examinations Duplex Surveillance 2026 · AIUM Practice Parameter 2022. For infrainguinal vein bypass, SVS 2018 recommends clinical examination, ABI and duplex at an early postoperative baseline, at 3, 6 and 12 months, and at least annually thereafter. Abnormal findings or new symptoms justify earlier reassessment; clinical triggers supplement scheduled surveillance SVS 2026. Duplex flags the at-risk graft by velocity, not symptoms alone: a focal peak systolic velocity above 300 cm/s with a velocity ratio above 3.5 across the lesion marks a high-grade, greater than 70% stenosis, while a uniformly low graft flow velocity below 45 cm/s signals a threatened graft; an intermediate lesion (PSV 180 to 300 cm/s, ratio 2.0 to 3.5) warrants shortened-interval reimaging. In post-EVAR surveillance, ultrasound effectively tracks sac size and endoleak presence, provided protocols mandate escalation to cross-sectional imaging when findings are technically limited or clinically discordant Chaer et al. (2009).

Hemodialysis access surveillance prioritizes bedside assessment. Routine clinical monitoring includes inspection, palpation, and auscultation at every dialysis session, escalating to specific interventions for triggers such as recirculation, abnormal pressures, or prolonged bleeding. Adjunctive duplex surveillance is conditionally suggested by KDOQI 2019 for high-risk circuits but has not consistently improved access survival in randomized trials, reserving its use for targeted evaluation of abnormalities rather than universal screening KDOQI 2019.

Venous evaluation pathways differ strictly by indication. For acute deep vein thrombosis (DVT), test validity relies on pretest probability; in outpatients classified as "DVT unlikely" with a negative high-sensitivity D-dimer, the 3-month venous thromboembolism event rate is 0.4% Wells 2003. For chronic venous disease, duplex quantifies insufficiency; pathologic deep venous reflux is confirmed under ESVS 2022 criteria when retrograde flow exceeds 1.0 second in the common femoral, femoral, and popliteal veins while standing after distal augmentation ESVS 2022.

7.4Areas of controversy

High-grade carotid stenosis velocity criteria are sensitive to equipment, patient mix, and laboratory practice. While a specific validation cohort identified PSV >= 450 cm/s or end-diastolic velocity >= 120 cm/s as the optimal threshold for >= 80% stenosis, its modest accuracy (AUC 0.66) demonstrates that exported, universal velocity thresholds lack precision without rigorous local laboratory validation Carotid Duplex Validation 2019.

The long-term utility of duplex surveillance for infrainguinal vein grafts is bounded by trial design. The primary endpoint analysis of the landmark VGST randomized trial occurred at 18 months, leaving late graft failure dynamics and the extended benefit of prolonged surveillance schedules incompletely defined VGST 2005.

The routine use of adjunctive duplex surveillance for hemodialysis accesses remains contested. Despite the physiological logic of detecting asymptomatic flow limitation, randomized trials fail to show consistent access-survival benefits, resulting in conditional recommendations that prioritize clinical monitoring at the dialysis session KDOQI 2019.

Further reading

• Editor's Choice - Duplex Ultrasound Surveillance after Infrainguinal Peripheral Artery Revascularisation: A Systematic Review with Narrative Synthesis. (2026). Duplex surveillance evidence and laboratory follow-up after infrainguinal revascularization; not native-carotid grading. Duplex Surveillance 2026