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Liver Shear-Wave Elastography

Shear-wave elastography quantifies liver stiffness as a surrogate for hepatic fibrosis, providing a non-invasive alternative to biopsy for staging chronic liver disease and monitoring progression or regression. An acoustic push pulse generates shear waves whose propagation speed increases with tissue stiffness; the result is reported in kilopascals or metres per second alongside strict quality metrics.

Indications

  • Staging and monitoring of fibrosis in chronic viral hepatitis B and C
  • Assessment of non-alcoholic/metabolic-associated fatty liver disease (NAFLD/MASLD)
  • Alcohol-related and autoimmune liver disease evaluation
  • Risk stratification for clinically significant portal hypertension and varices
  • Follow-up of treatment response and disease progression

Contraindications & Cautions

  • Unreliable in acute hepatitis, hepatic congestion (right heart failure) and cholestasis, which falsely raise stiffness
  • Ascites prevents shear-wave transmission from an intercostal window
  • Non-fasting state, food and recent alcohol transiently increase stiffness
  • Narrow intercostal spaces, obesity and inadequate breath-hold degrade measurement quality

Patient Preparation

  • Fast for at least 4-6 hours to avoid postprandial elevation of stiffness
  • Rest supine for several minutes before measurement
  • Right arm in maximal abduction behind the head to widen the intercostal spaces
  • Neutral breath-hold (avoid deep inspiration or Valsalva which alter values)
  • Record relevant liver enzymes, aetiology and BMI as confounders

Technique & Parameters

  • Curvilinear 1-6 MHz probe with 2D shear-wave or point shear-wave elastography
  • Intercostal approach through the right hepatic lobe (segments 5/8)
  • Place the region of interest at least 1.5-2 cm below the liver capsule, avoiding large vessels, ducts and rib shadowing
  • Acquire during a short neutral breath-hold with the probe perpendicular to the capsule
  • Obtain at least 10 valid measurements and report the median
  • Ensure quality: interquartile range/median ratio below 30% (below 15% for point SWE)

Systematic Review

  • Confirm adequate fasting, positioning and breath-hold before acquiring
  • Verify ROI depth, vessel-free placement and stable shear-wave map/propagation pattern
  • Assess measurement reliability using IQR/median and number of valid acquisitions
  • Interpret stiffness against system- and aetiology-specific thresholds
  • Correlate with grey-scale morphology, spleen size and Doppler signs of portal hypertension
  • Exclude confounders (congestion, inflammation, cholestasis, food) before staging

Key Findings & Significance

  • Rising liver stiffness (kPa) correlates with advancing fibrosis stage from F0 to F4
  • Values around or below ~5-6 kPa typically indicate absent or minimal fibrosis
  • Progressive elevation supports significant fibrosis (>=F2) and advanced fibrosis/cirrhosis (F3-F4)
  • Marked elevation raises concern for cirrhosis and clinically significant portal hypertension
  • High IQR/median or few valid measurements indicates an unreliable, non-diagnostic result
  • Discordantly high values in acute hepatitis or congestion reflect confounders, not fibrosis

Differential Considerations

  • Elevated stiffness: true fibrosis vs acute inflammation vs hepatic congestion vs cholestasis vs infiltration
  • Aetiology-specific thresholds differ (e.g. viral hepatitis vs MASLD), so cut-offs are not interchangeable
  • System dependence: values in kPa/m per second vary between transient elastography and 2D SWE vendors
  • Focal high stiffness within a mass suggests malignancy rather than diffuse fibrosis
  • Unreliable result: technical failure vs ascites vs narrow window vs poor breath-hold

Pearls & Pitfalls

  • Fasting and neutral breath-hold are essential; postprandial and deep-inspiration values are falsely high
  • Always report the aetiology and the specific system, since thresholds are vendor- and disease-specific
  • Reject measurements with IQR/median above the quality threshold rather than reporting an unreliable stage
  • Exclude congestion, acute hepatitis and cholestasis before attributing high stiffness to fibrosis
  • Combine elastography with grey-scale, spleen size and Doppler for portal hypertension assessment (Baveno criteria)

Structured Report

  • State technique (2D SWE vs pSWE), vendor/system, probe and fasting status
  • Report median stiffness in kPa (and/or m/s), number of valid measurements and IQR/median quality ratio
  • Interpret against the appropriate aetiology-specific thresholds and give an estimated fibrosis category
  • Note confounders that may affect reliability
  • Give an impression and recommend correlation with serum markers or follow-up as indicated

References

  • SRU Consensus Conference Statement on Liver Elastography (Barr RG et al., Radiology 2020)
  • EFSUMB Guidelines and Recommendations on the Clinical Use of Liver Ultrasound Elastography
  • AASLD Practice Guidance on Noninvasive Assessment of Liver Fibrosis
  • Ferraioli G et al. Liver Ultrasound Elastography: WFUMB Guidelines

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.