# Peripheral Arterial and Venous Disease Imaging

## Introduction

Peripheral vascular disease encompasses a spectrum of arterial and venous conditions that require multimodality imaging for diagnosis and management. **CT angiography (CTA), MR angiography (MRA), duplex ultrasound**, and catheter angiography each have distinct roles. This lecture reviews the imaging approach to peripheral arterial disease (PAD), deep venous thrombosis (DVT), and chronic venous insufficiency.

## Peripheral Arterial Disease

### Clinical Context

PAD affects approximately **8-12 million people** in the United States. Major risk factors include smoking, diabetes, hypertension, and hyperlipidemia. The **ankle-brachial index (ABI)** is the initial screening test, with an ABI less than 0.9 confirming PAD. The Fontaine classification stages PAD as Stage I (asymptomatic), Stage II (intermittent claudication), Stage III (rest pain), and Stage IV (tissue loss/gangrene). Imaging is indicated when revascularization is being considered.

### CT Angiography

CTA is the **first-line cross-sectional imaging** modality for PAD in many institutions. It offers high spatial resolution with rapid acquisition from the aorta to the feet, using a bolus tracking technique with timing tailored to ensure opacification of distal runoff vessels. Strengths include excellent assessment of **calcified plaque, stent evaluation, and surgical planning**. Limitations include dense arterial wall calcification that can obscure the lumen, as well as iodinated contrast and radiation exposure. **Multiplanar reformats and MIP images** are essential for complete evaluation.

### MR Angiography

**Contrast-enhanced MRA (CE-MRA)** with gadolinium is excellent for aortoiliac and femoropopliteal disease. **Time-resolved MRA** (TWIST, TRICKS) captures arterial and venous phases separately and is useful for calf vessels. **Non-contrast MRA** techniques include time-of-flight (TOF), quiescent-interval single-shot (QISS), and fresh blood imaging. MRA offers advantages of no radiation, no iodinated contrast, and no blooming from calcification, but has limitations including overestimation of stenosis, susceptibility artifacts from stents, and longer scan time. It is preferred in patients with **renal insufficiency**, using non-contrast techniques or reduced gadolinium dose.

### Duplex Ultrasound

| PSV Ratio | Stenosis Grade |
|-----------|---------------|
| <2.0 | <50% stenosis |
| >2.0 | >50% stenosis |
| >4.0 | >75% stenosis |
| Absent flow | Occlusion |

Duplex ultrasound is non-invasive, requires no contrast, is portable, and repeatable. It combines **B-mode imaging** with **spectral Doppler** and **color Doppler**. The **peak systolic velocity (PSV) ratio** is the primary metric for stenosis quantification: a PSV ratio greater than 2.0 indicates greater than 50% stenosis, a ratio greater than 4.0 indicates greater than 75% stenosis, and absent flow indicates occlusion. It is the first-line study for **post-bypass graft surveillance**. Limitations include operator dependence, limited assessment with large body habitus, and bowel gas interference over the iliac arteries.

![CTA of the lower extremities showing multisegmental peripheral arterial disease with occlusion of the SFA](images/peripheral-cta-pad.png)

### Catheter Angiography

Catheter angiography remains the **gold standard** for spatial resolution and allows simultaneous intervention. It is reserved for cases where percutaneous intervention is planned (angioplasty, stenting, atherectomy). Digital subtraction angiography (DSA) eliminates overlying bone and soft tissue. Carbon dioxide (CO2) angiography is an alternative in patients with severe contrast allergy or renal failure.

### Reporting for PAD

A **segmental approach** should be used: aortoiliac, common femoral, superficial femoral artery (SFA), popliteal, tibioperoneal trunk, anterior tibial, posterior tibial, and peroneal. The report should describe the degree of stenosis, length of disease, and presence of occlusion. **Runoff vessels** (patent tibial arteries supplying the foot) must be described because they determine the revascularization strategy. Relevant variants such as persistent sciatic artery or high origin of the anterior tibial artery should also be noted.

## Deep Venous Thrombosis (DVT)

### Compression Ultrasound

Compression ultrasound is the **gold standard** for the diagnosis of lower extremity DVT. The technique involves systematic compression of the veins in the transverse plane from the common femoral vein to the popliteal vein. The primary diagnostic criterion is **non-compressibility** of the vein. Additional findings include intraluminal echogenic thrombus, venous distension, and absent color or spectral Doppler flow. Augmentation maneuvers (calf squeeze) assess flow in proximal veins. **Sensitivity and specificity exceed 95%** for proximal DVT (above the knee).

### Acute versus Chronic DVT

| Feature | Acute DVT | Chronic DVT |
|---------|-----------|-------------|
| Vein caliber | Distended | Small/normal |
| Thrombus echogenicity | Anechoic/hypoechoic | Echogenic |
| Vessel walls | Smooth | Thickened |
| Other findings | None | Intraluminal synechiae, collaterals, recanalization channels |

**Acute DVT** presents with a distended vein, anechoic or hypoechoic thrombus, and smooth vessel walls. **Chronic DVT** shows a small-caliber vein, echogenic thrombus, thickened vessel walls, intraluminal synechiae, and collateral veins. **Recanalization** of chronic thrombus shows irregular channels within the vein.

### Upper Extremity DVT

Upper extremity DVT is increasingly common due to central venous catheter use and thoracic outlet syndrome. The same ultrasound technique is applied with compression of the internal jugular, subclavian, axillary, and brachial veins. The subclavian vein may be difficult to compress due to the overlying clavicle, requiring reliance on Doppler assessment. **Paget-Schroetter syndrome** refers to effort-related thrombosis of the axillary-subclavian vein in young athletes.

![Compression ultrasound demonstrating non-compressible common femoral vein with acute DVT](images/peripheral-dvt-compression-us.png)

### CT Venography and MR Venography

**CT venography** is acquired as a delayed phase after CTA or as a standalone study and identifies pelvic and IVC thrombus not accessible by ultrasound. **MR venography** uses non-contrast techniques (TOF, balanced SSFP) or contrast-enhanced approaches and is useful for suspected IVC, pelvic, or upper extremity DVT. May-Thurner syndrome (left common iliac vein compression by the right common iliac artery) is best demonstrated by MRV or CT.

## Chronic Venous Insufficiency

Chronic venous insufficiency results from **valvular incompetence** and/or prior DVT (post-thrombotic syndrome). Duplex ultrasound with the patient standing is the primary study. **Reflux** is defined as retrograde flow lasting greater than **0.5 seconds** in superficial veins and greater than **1.0 second** in deep veins. The distribution of reflux should be mapped across the great saphenous vein (GSV), small saphenous vein (SSV), perforator veins, and deep veins. Pre-operative mapping guides thermal ablation, sclerotherapy, or surgical stripping.

![Duplex ultrasound showing venous reflux in the great saphenous vein with prolonged retrograde flow](images/peripheral-venous-reflux-us.png)

## Key Clinical Pearls

**Non-compressibility** on ultrasound is the single most important criterion for DVT diagnosis. CTA is the most commonly used cross-sectional modality for PAD evaluation, but dense calcification can limit luminal assessment. In PAD imaging, always report the status of **tibial runoff vessels** as this determines whether the patient is a candidate for bypass or endovascular therapy. MRA is preferred over CTA in patients with renal insufficiency, using non-contrast techniques when possible.

## References

1. ACR Appropriateness Criteria: Peripheral Arterial Disease. *J Am Coll Radiol*. 2019;16(5S):S375-S383.
2. Lower Extremity DVT: Current Imaging Strategies. *Radiographics*. 2018;38(4):1128-1148.
3. Society for Vascular Surgery Clinical Practice Guidelines for Lower Extremity PAD. *J Vasc Surg*. 2015;61(3S):2S-41S.
4. Chronic Venous Insufficiency: Imaging Assessment and Treatment Options. *Radiol Clin North Am*. 2020;58(4):707-722.