Vascular Diagnostics and Imaging

Background

Summary: This chapter provides a comprehensive overview of diagnostic modalities in vascular surgery, ranging from bedside clinical examination to advanced imaging techniques and emerging artificial intelligence applications. The diagnostic approach must balance accuracy, safety, cost-effectiveness, and availability while adhering to evidence-based guidelines from major vascular societies. ^{[1] [2] [3] [4]}

Clinical Examination

Still fundamental despite imaging advances.

• Arterial disease: pulse palpation, bruits, trophic changes, Buerger’s test.
• Venous disease: Trendelenburg and Perthes tests (historic), now complemented by DUS.
• Lymphatic disease: inspection for edema, Stemmer’s sign.
• Limitations: subjective, low sensitivity in early disease, cannot localize lesions precisely. ^{[1] [5] [6]}

Ankle-Brachial Index

• Definition: ratio of ankle systolic pressure to brachial systolic pressure.
• Normal values: 1.00–1.40.
• PAD diagnosis: <0.90 indicates peripheral arterial disease; <0.50 indicates severe ischemia.
• Noncompressible arteries: Values >1.40 suggest medial arterial calcification (common in diabetes and chronic kidney disease). In such cases, measure toe pressures and toe-brachial index instead.
• Exercise testing: If symptoms suggest PAD but resting ABI is normal, perform post-exercise ABI. A decrease ≥20% in ABI or ≥30 mmHg drop in ankle pressure supports the diagnosis.
• Guidelines: AHA/ACC (2016) and ESC (2017) recommend ABI as first-line screening, with exercise ABI and TBI when indicated. ^{[7] [2] [8] [9]}

Toe-Brachial Index

• Advantage: less affected by medial calcification.
• Useful: diabetes, elderly, dialysis patients.
• Cutoff: <0.7 = PAD. ^{[9] [7] [2]}

Segmental Pressure Measurements

• Performed at thigh, calf, ankle.
• A drop >20 mmHg suggests significant stenosis proximal to site. ^{[2] [1]}

Pulse Volume Recordings

• Provides waveform analysis of volume changes.
• Flattened waveforms = severe PAD.
• Advantage: not affected by calcification. ^{[2] [1]}

Transcutaneous Oxygen Pressure (TcPO₂)

• Assesses skin oxygenation, predicts wound healing.
• >50 mmHg = good healing potential.
• <20 mmHg = poor healing potential. ^{[10] [11]}

Venous Plethysmography

• Air plethysmography: quantifies reflux and obstruction.
• Replaced by duplex in many centers but still used in research. ^[5]

Duplex Ultrasound

• Principle: Combines B-mode imaging with Doppler waveform analysis to provide both anatomic and hemodynamic information.
• Applications:
• Carotid artery stenosis grading (using NASCET and ESVS criteria); see 7Ch. 7 for complete grading tables and management thresholds.
• PAD severity assessment and lesion localization.
• AAA diameter measurement and surveillance; see 4Ch. 4 for screening/surveillance protocols.
• Venous disease: reflux assessment (valve incompetence) and thrombosis detection (DVT).
• Post-intervention graft surveillance (e.g., after bypass surgery or EVAR).
• Advantages: Portable, non-invasive, relatively inexpensive, and repeatable without radiation or nephrotoxic contrast.
• Limitations: Operator-dependent technique with reduced accuracy in obesity, presence of bowel gas, or extensive vascular calcification.
• Guidelines: Recommended as first-line imaging for carotid disease, venous disease, and AAA surveillance. ^{[12] [13] [14] [3] [15] [16] [17]}

Computed Tomography Angiography

• Gold standard for aortic disease (AAA, TAAA, TEVAR planning).
• Technical essentials: Submillimeter collimation (≤1 mm), multiphasic acquisition (non-contrast, arterial phase with bolus-tracking, delayed phase for endoleak detection), ECG-gating for thoracic aorta when assessing root or ascending segments, standardized contrast delivery (4–6 mL/s) with saline chaser, and iterative reconstruction algorithms to reduce radiation dose.
• Applications:
• AAA and TAAA morphology assessment and access vessel evaluation; see 4Ch. 4 for measurement standards and repair thresholds.
• EVAR and TEVAR planning and surveillance.
• Carotid and aortic arch assessment; see 7Ch. 7 for carotid imaging protocols.
• Peripheral arterial disease mapping.
• Surveillance protocols: Baseline CTA at 30 days post-procedure, follow-up at 12 months, then individualized surveillance based on aneurysm sac behavior and endoleak status. Consider duplex ultrasound or contrast-enhanced ultrasound (CEUS) in patients with stable anatomy or renal insufficiency.
• Limitations: Ionizing radiation exposure and iodinated contrast risks (nephropathy, allergic reactions).
• Guidelines: ESVS AAA (2019) and ESVS carotid (2018) guidelines recommend CTA as a primary planning tool, with aneurysm and post-repair imaging surveillance tailored to patient and device factors. ^{[18] [3] [14] [19] [17]}

Magnetic Resonance Angiography

• Advantages: No ionizing radiation and excellent soft tissue contrast.
• Techniques: Time-of-flight (TOF), contrast-enhanced MRA (CE-MRA), and non-contrast MRA options for patients with renal insufficiency or contrast allergy. Vessel-wall imaging sequences provide enhanced characterization of vasculitis and arterial dissection.
• Applications:
• Carotid and intracranial disease.
• Aortic pathology, particularly in connective tissue disorders.
• Renal artery stenosis.
• Peripheral arterial disease mapping when CTA is unsuitable.
• Limitations: Limited availability, higher cost, and contraindications including certain metallic implants, pacemakers, and claustrophobia.
• Guidelines: Recommended as alternative first-line imaging when CTA is contraindicated; modality choice should be guided by specific disease characteristics and patient factors. ^{[20] [2] [8] [14] [3]}

Catheter Angiography (Digital Subtraction Angiography, DSA)

• Historically the gold standard.
• Now reserved for interventional procedures (angioplasty, stenting, embolization).
• Advantages: real-time imaging, therapeutic capability.
• Limitations: invasive, risk of complications (bleeding, dissection, contrast nephropathy). ^{[21] [2]}

Intravascular Ultrasound

• Provides lumen size, wall characteristics, and stent apposition assessment.
• Widely used in endovascular aneurysm repair and iliac vein stenting.
• Venous applications: In iliofemoral venous obstruction, venography often underestimates lesion severity. IVUS improves detection of non-thrombotic iliac vein lesions and optimizes stent sizing and landing zone selection.
• Arterial applications: In aorto-iliac and femoropopliteal interventions, IVUS confirms vessel sizing, stent apposition, and detects complications such as dissection or underexpansion.
• SVS guidelines: reasonable adjunct in complex endovascular repair. ^{[22] [23] [19]}

Optical Coherence Tomography

• Ultra-high resolution (10–20 μm).
• Limited penetration depth; mostly used in coronary arteries, but research ongoing for peripheral applications. ^[23]

PET/CT and PET/MR

• Indications:
• (1) Large-vessel vasculitis/polymyalgia rheumatica—FDG PET/CT(A) supports diagnosis, maps extent, and monitors response per EANM/EULAR recommendations.
• (2) Suspected vascular graft/endograft infection—FDG PET/CT (and WBC SPECT/CT) complements CT to improve diagnostic accuracy and delineate extent per ESVS VGEI guidelines.
• Limitations: cost, access, radiation, and need for standardized protocols. ^{[24] [25]}

Artificial Intelligence (AI) in Diagnostics

• Automated ABI/DUS interpretation.
• CTA segmentation for aneurysm planning.
• Predictive models for rupture risk and outcome.
• Growing role in personalized vascular medicine. ^[4]

Tables

Table 3.1. Comparison of Diagnostic Modalities

Exercise ABI, post-exercise testing, and handling noncompressible arteries

Exercise ABI and Noncompressible Arteries

When clinical symptoms suggest peripheral arterial disease but the resting ABI is normal, post-exercise testing should be performed using treadmill or heel-raise protocols. A decrease in ABI ≥20% or an ankle pressure drop ≥30 mmHg after exercise supports the diagnosis of PAD. ^{[7] [2]}

An ABI >1.40 indicates noncompressible arteries due to medial arterial calcification. In such cases, toe systolic pressure and toe-brachial index (TBI) should be measured, as these metrics are less affected by calcification. A toe pressure <30 mmHg suggests severe ischemia in chronic limb-threatening ischemia (CLTI). ^{[9] [26] [11]}

Objective perfusion metrics for CLTI: toe pressure, TcPO2, skin perfusion pressure (SPP) and WIfI staging

Objective Perfusion Metrics for CLTI: Toe Pressure, TcPO₂, Skin Perfusion Pressure (SPP), and WIfI Staging

In patients with chronic limb-threatening ischemia (CLTI), objective perfusion measurements are essential for assessing disease severity and predicting wound healing potential. ^[11]

Key metrics and thresholds (per WIfI):

• Toe pressure: <30 mmHg indicates severe ischemia (WIfI I2–I3); 30–39 mmHg moderate (I1); ≥40 mmHg adequate (I0).
• Transcutaneous oxygen pressure (TcPO₂): <30 mmHg indicates severe ischemia with poor healing potential (WIfI I2–I3); 30–39 mmHg moderate (I1); ≥40 mmHg adequate perfusion favorable for wound healing (I0).
• Skin perfusion pressure (SPP): <30–40 mmHg indicates poor healing potential.

These perfusion parameters should be integrated into the Society for Vascular Surgery Wound, Ischemia, and foot Infection (WIfI) staging system and applied according to Global Vascular Guidelines (GVG) recommendations for revascularization planning. See 10Ch. 10 for complete WIfI classification and management. ^{[26] [11] [9] [10]}

Standardized duplex ultrasound protocols and criteria

Standardized Duplex Ultrasound Protocols and Criteria

Standardized protocols and interpretation criteria are essential for reliable duplex ultrasound assessment:

• Carotid artery stenosis: Stenosis severity is graded using peak systolic velocity (PSV) and internal carotid artery/common carotid artery (ICA/CCA) ratio. Laboratory-validated thresholds should be used, typically PSV ≥125 cm/s for ≥50% stenosis and ≥230 cm/s for ≥70% stenosis according to consensus criteria. Reports should include plaque morphology and contralateral disease status.
• Lower extremity arterial disease: Assessment includes PSV, velocity ratios (VR) across lesions, and waveform analysis. Velocity ratio thresholds help identify hemodynamically significant stenoses, with documentation of inflow, outflow, and runoff status.
• Post-intervention surveillance: Graft surveillance employs specific thresholds, with high PSV and velocity ratios indicating stenosis and low graft PSV suggesting risk of thrombotic failure. EVAR surveillance protocols integrate duplex findings with cross-sectional imaging.

These protocols align with ESVS carotid guidelines and Society of Radiologists in Ultrasound (SRU) consensus statements. ^{[13] [14] [12]}

CTA technical parameters for aorta and peripheral arteries

CTA Technical Parameters for Aorta and Peripheral Arteries

Optimal CTA imaging requires attention to specific technical parameters that vary by anatomic region:

Aortic and EVAR imaging: High-quality aortic CTA employs submillimeter collimation (≤1 mm) with multiphasic acquisitions including non-contrast, arterial phase (using bolus tracking), and delayed phase for endoleak detection. ECG-gating is applied for thoracic aorta imaging when assessing the aortic root or ascending aorta. Standardized contrast delivery protocols (4–6 mL/s with bolus tracking) ensure consistent arterial enhancement.

Lower extremity CTA: Imaging parameters including table speed and reconstruction kernels are optimized for distal runoff vessel assessment, ensuring adequate visualization of tibial and pedal arteries.

These technical standards support the planning and surveillance protocols outlined in ESVS AAA guidelines. ^{[18] [3]}

MRA advances for PAD and aorta (non-contrast techniques, vessel wall imaging)

MRA Advances for PAD and Aorta: Non-Contrast Techniques and Vessel Wall Imaging

Magnetic resonance angiography has evolved to include multiple technique options that expand its clinical applicability:

Non-contrast MRA techniques: When gadolinium-based contrast is contraindicated (e.g., severe renal insufficiency, prior allergic reaction), non-contrast MRA sequences provide viable alternatives for vascular imaging. These include time-of-flight (TOF) and various flow-based techniques that do not require exogenous contrast agents.

Contrast-enhanced MRA: Where safe, CE-MRA remains the preferred MR technique, offering superior image quality and faster acquisition times compared to non-contrast methods.

Vessel wall imaging: Specialized MR sequences enable direct visualization of the arterial wall, proving particularly valuable in diagnosing and monitoring large vessel vasculitis and characterizing arterial dissection. These techniques provide information beyond luminal assessment alone.

MRA serves as an alternative first-line imaging modality in patients for whom CTA is inappropriate, with modality selection guided by disease characteristics and patient-specific factors according to major PAD and disease-specific guidance. ^{[20] [2] [3] [14]}

Intravascular imaging: IVUS for iliac venous outflow obstruction and arterial optimization; OCT scope

Intravascular Imaging: IVUS for Iliac Venous Outflow Obstruction and Arterial Optimization; OCT Scope

Intravascular ultrasound (IVUS) has become an important adjunctive imaging modality in both venous and arterial interventions:

Venous applications: In iliac venous disease, IVUS demonstrates superior sensitivity compared to venography for identifying non-thrombotic lesions, particularly May-Thurner syndrome and other extrinsic compression syndromes. IVUS guidance optimizes stent sizing and landing zone selection, and is routinely recommended for iliofemoral venous stenting procedures.

Arterial applications: During aortoiliac and femoropopliteal interventions, IVUS assists with accurate vessel sizing and identifies procedural complications including arterial dissection and stent underexpansion that may not be apparent on angiography alone.

Optical coherence tomography (OCT): While OCT provides higher resolution imaging than IVUS (10–20 μm), its clinical application in peripheral vascular surgery remains largely investigational, with selective use in specific research protocols and niche clinical scenarios. ^{[22] [23] [19]}

Nuclear medicine: PET/CT for large-vessel vasculitis and vascular graft/endograft infection

Nuclear Medicine: PET/CT for Large-Vessel Vasculitis and Vascular Graft/Endograft Infection

Positron emission tomography combined with computed tomography (PET/CT) has established specific indications in vascular surgery:

Large-vessel vasculitis and polymyalgia rheumatica: Fluorodeoxyglucose (FDG) PET/CT or PET/CTA improves diagnostic confidence in suspected vasculitis, maps disease extent throughout the vascular tree, and assesses disease activity. This modality is particularly valuable in large-vessel vasculitis involving the aorta and its major branches, where conventional imaging may be inconclusive.

Vascular graft and endograft infection: FDG PET/CT and radiolabeled white blood cell (WBC) SPECT/CT provide functional imaging that complements anatomic CT findings. These modalities improve diagnostic accuracy for prosthetic graft infection and help delineate the extent of infection to guide surgical planning.

These applications are supported by European Association of Nuclear Medicine (EANM) procedural recommendations and ESVS vascular graft and endograft infection guidelines. ^{[24] [25]}

Contrast-enhanced ultrasound (CEUS) for EVAR surveillance

Contrast-Enhanced Ultrasound (CEUS) for EVAR Surveillance

Contrast-enhanced ultrasound utilizes intravenous microbubble contrast agents to enhance ultrasound signal and improve visualization of blood flow. In the context of EVAR surveillance, CEUS demonstrates high sensitivity for detecting endoleaks, particularly type II endoleaks that may be subtle on conventional imaging.

CEUS serves as a valuable adjunct to CTA in EVAR surveillance protocols, offering several advantages including lack of ionizing radiation and use of non-nephrotoxic contrast agents. This makes CEUS particularly useful in patients with renal insufficiency or those requiring frequent surveillance imaging, where cumulative radiation exposure and contrast load are concerns.

The role of CEUS in EVAR surveillance is outlined in major AAA guideline recommendations, which recognize its utility in selected patient populations. ^{[3] [17]}