What is liver elastography?

What is Liver Elastography?

Liver elastography is a noninvasive imaging technique that measures liver stiffness as a surrogate biomarker for liver fibrosis by generating mechanical or acoustic vibrations through the liver and quantifying the elastic properties of the hepatic parenchyma. 1

Core Principle and Mechanism

Elastography works by measuring how quickly shear waves propagate through liver tissue—stiffer (more fibrotic) livers transmit waves faster than normal livers. 2, 3 The technique quantifies the elastic/shear modulus of liver parenchyma, which serves as a surrogate marker for the degree of fibrosis present in chronic liver disease. 1

Three Main Types of Liver Elastography

Transient Elastography (TE/VCTE)

• Most commonly used method in clinical practice, performed with devices like FibroScan at bedside during clinic visits without additional equipment. 1
• A probe is applied to the intercostal skin in the 9th to 11th intercostal space, generating mechanical vibrations that create shear waves through a region 25-65 mm (M-probe) or 35-75 mm (XL-probe) below the skin surface. 1
• Requires a minimum of 10 valid liver stiffness measurements to derive a composite score, with adequate quality defined as ≥10 validated measurements and interquartile range/median value ≤30%. 1
• Results are expressed in kilopascals (kPa), ranging from 2.5-75 kPa, with higher values indicating greater liver stiffness and more advanced fibrosis. 1, 4
• Has the largest body of evidence supporting its use across multiple liver disease etiologies. 1

Shear Wave Elastography (SWE/ARFI)

• Uses acoustic radiation force impulse imaging to generate shear waves through acoustic vibrations rather than mechanical vibrations. 1, 2
• Can be combined with conventional ultrasound and performed in patients with obesity, ascites, and NAFLD where TE may fail. 1
• Allows selection of specific larger areas of the liver for study compared to TE's single-element transducer. 1
• Has lower failure rates than TE (2.1% vs 6.6%, P<0.001), particularly in obese patients. 1

Magnetic Resonance Elastography (MRE)

• Appears to be the most accurate method for detecting liver fibrosis across various disease etiologies. 1
• Permits assessment of the whole liver rather than a limited sampling area, reducing sampling error. 1
• Measures the magnitude of the complex shear modulus by directly visualizing propagating shear waves through the liver. 2, 5
• Particularly advantageous in NAFLD, where it demonstrates higher accuracy than ultrasound-based methods. 1

Diagnostic Performance

Overall Accuracy

• For significant fibrosis (F2-4): Sensitivities range from 51-95%, specificities from 36-100% across all techniques and diseases. 1
• For advanced fibrosis (F3-4): Sensitivities range from 70-100%, specificities from 74-100%. 1
• For cirrhosis (F4): Sensitivities range from 60-100%, specificities from 67-99%. 1
• Accuracy increases progressively from F2-4 to F3-4 and is highest for F4 (cirrhosis). 1

Specific Performance in Hepatitis C

• VCTE demonstrates sensitivity of 0.89 (95% CI 0.84-0.92) and specificity of 0.91 (95% CI 0.89-0.92) for diagnosing cirrhosis. 1
• For significant fibrosis, TE has sensitivity of 70% and specificity of 84%; for cirrhosis, sensitivity of 87% and specificity of 91%. 1

Critical Confounding Factors and Limitations

Technical Limitations

• Obesity: TE may fail in patients with BMI >28 kg/m², though XL-probes are now available for obese patients. 1
• Ascites: Cannot be performed reliably in patients with ascites. 1
• Narrow intercostal spaces: May prevent adequate probe placement. 1
• Failure rates range from 1.1-3.5% in Asian populations and 4.3-10.5% in Western populations, primarily due to body habitus differences. 1

Clinical Confounders That Falsely Elevate Stiffness

• Active hepatitis/inflammation: Can produce falsely cirrhotic-range values that do not reflect true fibrosis. 1, 6
• Recent food intake: Food ingestion within 2-4 hours falsely elevates liver stiffness values regardless of measurement method. 1, 6
• Alcohol abuse: Recent alcohol consumption can falsely elevate measurements. 1, 4
• Vascular congestion: Right heart failure causes passive congestion that increases stiffness independent of fibrosis. 1, 6
• Extrahepatic cholestasis: Obstructive cholestasis artificially increases stiffness measurements. 1, 6

Important Caveats

• Stiffness values can decrease immediately following successful treatment (e.g., antiviral therapy, alcohol cessation) without corresponding improvement in fibrosis, reflecting resolution of inflammation rather than fibrosis regression. 1
• Cutoff values for estimating fibrosis stage vary depending on liver disease etiology and differ between adults and children. 1
• Elastography measures stiffness, not inflammation or alternative diagnoses—it cannot rule out other causes of liver disease. 4

Clinical Applications Beyond Fibrosis Staging

• Predicting liver decompensation risk and clinical outcomes in patients with cirrhosis. 1, 2
• Differentiating NASH from simple steatosis in patients with fatty liver disease. 2
• Monitoring response to treatment in chronic liver disease, though changes may reflect inflammation resolution rather than fibrosis improvement. 1
• Stratifying patients prior to antifibrotic treatment and tracking hepatic inflammation and fibrosis over time. 1

Comparison to Liver Biopsy

Elastography has emerged as the preferred noninvasive alternative to liver biopsy, which has significant limitations including invasiveness, pain in up to 30% of patients, severe bleeding in <1% of cases, hospitalization requirements in 2-3% of patients, and mortality rate up to 0.33%. 1 Additionally, liver biopsy suffers from sampling error and both intra-observer and inter-observer variability in interpretation, with fibrosis assessment differing by at least one stage in approximately 25% of chronic HCV patients when two independent biopsies are obtained. 1 Elastography is also easier to repeat for serial assessments over time. 1