Duplex Ultrasound Protocol Post EVAR

Duplex is a first-line, non-invasive modality for post-EVAR surveillance, particularly for:

Non-invasive surveillance to detect endoleaks, assess graft integrity, monitor aneurysm sac behavior, and guide management.

• Endoleak detection

• Graft patency

• Aneurysm sac behavior (expansion vs regression)

1. Protocol Overview

Patient Position

• Supine, NPO, with Gas-X, 2 tabs the night before and 2 tab the morning of exam

• Right and left lateral decubitus may improve iliac imaging

• Slight reverse Trendelenburg can improve sac visualization

Equipment

• Curvilinear array transducer (1–5 MHz)

• Color Doppler and spectral Doppler modes

2. Protocol and Views

✅ A. Aneurysm Sac

• Scan in gray scale (longitudinal & transverse)

• Measure maximum anterior-posterior (AP) and transverse sac diameter

• Compare with baseline (post-op or pre-op imaging)

• >5 mm sac enlargement = suspect endoleak, graft issue or endotension or graft failure

• Echolucient zones suggest leak or fluid

• Mural thrombus

• Wall irregularity or pulseatility

✅ B. Endograft Integrity and Surveillance

• Visualize entire main body & both iliac limbs

• Use Color Doppler to assess patency

• Check for: Migration (compare graft end position to landmarks)

• Kinking or stenosis

• Limb occlusion (absent or reduced flow)

• Disconnection (type III concern)

• Check graft position: any signs of migration, kinking, or fracture?

• Are all limbs visible? Any occlusion?

✅ C. Color and Spectral Doppler Assessment

Color Doppler:

• Look for pulsatile flow within the sac (sign of endoleak)

• Use low flow settings for slow leaks (Type II)

Spectral Doppler:

• Characterize flow as arterial vs. venous

• Identify "to-and-fro" pattern → classic for Type II

• Sample proximal & distal ends for high-velocity jets → Type I

• May detect low-flow endoleaks missed by CT

3. Surveillance Schedule (Typical)

Post-EVAR Imaging

• 1 month: CTA ± Duplex

• 6 months: Duplex

• 12 months: CTA ± Duplex

• Annually if stable: Duplex

Some centers alternate CTA and Duplex for long-term surveillance, especially in favorable anatomy or renal insufficiency.

Endoleaks: Types, Appearance, and Management

There are 5 types of endoleaks. Duplex can detect most types, though CTA/CEUS is better in some cases.

Type I – Inadequate Seal (attachment site)

Source: Proximal (Ia) or Distal (Ib) end of graft
Duplex finding: High-velocity flow at graft attachment site entering sac
Risk: High rupture risk
Management: Urgent repair – ballooning, cuff extension, or open conversion

Type II – Retrograde Flow into Sac

Source: Lumbar, IMA, or accessory arteries
Duplex finding: To-and-fro or low-velocity flow into sac; may be delayed
Common? Most common (up to 30–40%)
Management:

• Observe unless:

  • Sac growth >5 mm

  • Persistent >6–12 months

• Then consider embolization (transarterial or translumbar)

Type III – Graft Defect (junction or fabric tear)

Source: Modular disconnection or fabric failure
Duplex finding: High-velocity turbulent flow into sac, not from attachment zones
Risk: High rupture risk
Management: Urgent repair – bridging stents, relining, or open conversion

Type IV – Graft Porosity (rare)

Source: Graft material porosity (seen in older devices)
Duplex finding: Usually not seen – needs CTA
Management: Often resolves spontaneously

Type V – Endotension (no visible leak)

Definition: Continued sac expansion without visible leak
Diagnosis: Diagnosis of exclusion
Duplex finding: No color flow, but sac continues to grow
Management: Controversial: options include open conversion, relining, or continued surveillance

Summary: What to Look for on Duplex Post-EVAR

• Flow within aneurysm sac → Suspect endoleak

• Enlarging sac >5 mm → Evaluate for Type I, II or III endoleak

• High velocity at proximal/distal ends → Suggests Type I

• To-and-fro low flow → Classic for Type II

• Disrupted graft with turbulent flow → Suggests Type III

• Sac growth but no flow → Consider endotension (Type V)
  
  

  

  Alert Criteria

  • Sac growth >5 mm

  • New or persistent sac flow

  • Suspicion of Type I/III endoleak

  • Limb occlusion

  Optimization

  Goal: Maximize sensitivity for detecting low-velocity, slow-volume flow in or around the aneurysm sac.

  1. Grayscale Optimization

  • Frequency: Use lower frequencies (1–5 MHz) for deep penetration

  • Depth: Focus just beyond the aneurysm sac

  • Focal Zone: Set at or just below the sac

  • Gain: Increase until background noise appears, then reduce

  • TGC: Brighten posterior sac if needed

  • Dynamic Range: Wide range to distinguish structures and thrombus

  2. Color Doppler Optimization

  Key Settings to Adjust:

  • Color Gain: High (just below noise threshold)

  • PRF: Very Low (5–15 cm/s)

  • Wall Filter: Lowest possible

  • Box Size: Small & focused over sac

  • Color Map: Use contrast-enhancing maps (red-blue or variance)

  • Persistence: Medium–high

  • Steering: Apply to optimize angle relative to graft flow

  Tip: Start with a low PRF (~7–10 cm/s), then increase if too much background noise appears.

  3. Spectral Doppler Optimization

  • Sample Gate Size: Small (1–2 mm)

  • Gain: Increase until background noise, then back off

  • Sweep Speed: Medium to slow

  • Angle Correction: Apply only when measuring known flow direction

  Look for:

  • High-velocity jets (Type I/III)

  • To-and-fro pattern (Type II)

  4. Techniques to Enhance Leak Detection

  • Valsalva Maneuver

  • Graded abdominal compression

  • Left lateral decubitus

  • Reverse Trendelenburg

  • Re-scan sac after contrast or Doppler delay

  • CEUS if inconclusive

  ✅ Quick Troubleshooting Tips

  • Can’t see sac clearly → Adjust depth, gain, focal zone

  • No flow detected → Lower PRF, raise color gain

  • Too much flash/noise → Increase wall filter or decrease gain

  • Suspected leak but unclear → Try CEUS or delayed scanning

  Summary Checklist: Color Doppler Optimization for Endoleak

  • Color Gain → Max before noise

  • PRF → As low as ~5–10 cm/s

  • Wall Filter → Set to minimum

  • Focus → Centered at sac depth

  • Box Size → Minimized to target area

  • Map & Persistence → Chosen for contrast and smoothing

  • Spectral Sample → Small gate, slow sweep

  • Dynamic Maneuvers → Valsalva, repositioning
    
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