Liver Elastography: Reading the Liver Between the Waves

Introduction

Chronic liver disease (CLD) progresses through fibrosis → cirrhosis, irrespective of etiology (viral, alcohol, NAFLD, autoimmune). Accurate staging of fibrosis is essential for:

• Prognosis
• Treatment planning
• Monitoring disease progression

Traditionally, liver biopsy is the gold standard, but it is invasive and limited by sampling error. Hence, elastography has emerged as a non-invasive, reliable alternative.

Need for Elastography

Limitations of Liver Biopsy

• Invasive, risk of haemorrhage
• Sampling error (heterogeneous fibrosis)
• Interobserver variability
• Not suitable for follow-up

Limitations of Conventional Imaging

• CT/MRI/US detect late cirrhosis only
• Poor sensitivity for early fibrosis

Hence, elastography bridges the gap by quantifying tissue stiffness.

Basic Principle of Elastography

Elastography measures tissue stiffness based on:

• Stress → applied force
• Strain → tissue deformation

Fibrotic liver = stiffer tissue → faster wave propagation

Types of Liver Elastography

Ultrasound-Based Elastography:

1. Strain Elastography

   • Uses manual compression
   • Qualitative (colour map)
   • Limited role in the liver

Strain elastography shows a complex cystic-solid lesion with mixed stiffness – the solid component appears stiff (red) and cystic component appears soft (blue).

2. Transient Elastography (FibroScan)

   • Uses mechanical vibrator (50 Hz)
   • Measures stiffness in kPa
   • No real-time imaging

Advantages:

• Fast (<5 min)
• Bedside technique

Limitations:

• Not usable in ascites
• Limited in obesity
• No B-mode guidance

3. Point Shear Wave Elastography (pSWE)

   • Uses acoustic radiation force impulse (ARFI)
   • Measures velocity (m/s)
   • ROI-based

1. 2D Shear Wave Elastography

   • Real-time colour elastogram
   • Larger ROI
   • Better spatial mapping

MR Elastography (MRE)

• Uses mechanical waves (60 Hz)
• Measures shear modulus (kPa)
• Produces:
  • Wave images
  • Elastogram (stiffness map)

MR elastography setup showing an external acoustic wave generator transmitting vibrations via tubing to a passive driver placed on the patient’s abdomen.

Technique

US Elastography

• Supine/left posterior oblique position
• Right lobe via intercostal approach
• Breath-hold (end expiration)
• 10–12 measurements; median value used

MR Elastography

• Passive driver over the right lobe
• 4 axial slices acquired
• ROI avoids capsule, vessels, artifacts

Interpretation

US Elastography

• Low → F0–F1
• Intermediate → F2–F3
• High → F4 (cirrhosis)
• Machine-dependent cutoffs

MR Elastography (kPa)

• <2.5: Normal
• 2.5–2.9: Inflammation
• 2.9–3.5: F1–F2
• 3.5–4.0: F2–F3
• 4–5: F3–F4
• 5: Cirrhosis

Confounding Factors

Technical

• Incorrect ROI
• Left lobe (false high)
• Depth > 7 cm (false low)
• Inclusion of vessels/capsule

Biological

• Inflammation
• Congestion
• Postprandial state
• Alcohol

Clinical Applications

• Fibrosis staging
• Treatment monitoring
• Portal hypertension prediction
• NAFLD/NASH evaluation
• Transplant assessment

Advantages & Limitations

Advantages

• Non-invasive, repeatable
• Large sampling volume
• Early fibrosis detection

Limitations

• Operator-dependent (US)
• Lack of standardization
• Cost (MRE)
• Cannot determine etiology

Future Directions

• Spleen stiffness for portal HTN
• Tumour characterization
• Fibrosis vs inflammation differentiation
• Prognostic biomarker

Conclusion

Elastography is a non-invasive, accurate, and reproducible tool for liver fibrosis assessment, reducing reliance on biopsy.

Dr Kanagasabai Kamalasekar
Consultant Radiology,
Kauvery Hospital, Chennai

Dr Malavika S
DNB Radiology Resident,
Kauvery Hospital, Chennai