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What is transient elastography?
Transient elastography is an imaging medical test used to determine the stiffness of liver tissue, a key marker for liver fibrosis (scarring). The test is commonly used to assess the condition of the liver of individuals suffering from chronic liver diseases, e.g., non-alcoholic fatty liver disease (NAFLD), hepatitis, or cirrhosis. The test is less invasive than liver biopsy in the assessment of liver fibrosis and can help determine the degree of liver injury.
Here’s a summary of transient elastography:
1. How Transient Elastography Works
Transient elastography uses a vibration technique to measure the stiffness of liver tissue.
During the procedure, a special probe called a FibroScan® is placed on the skin over the liver, typically on the right upper abdomen.
The probe introduces a burst of vibration (an elastic wave) into the liver tissue. The speed at which the wave travels in the liver is measured.
If the waves travel faster, it indicates that the tissue is more rigid, which typically is a sign of fibrosis (liver scarring). If the waves travel slower, it suggests healthier, more compliant liver tissue.
2. What It Measures
Liver stiffness is measured in kilopascals (kPa), a unit of liver elasticity.
A firm liver will tend to indicate a higher level of fibrosis or scarring and often accompanies disease like cirrhosis.
Results provide an estimate of the level of fibrosis in the liver, and doctors can make a judgment about the extent of liver damage without the need for an invasive test like a liver biopsy.
3. Advantages of Transient Elastography
Not invasive: A liver biopsy involves tissue sampling but transient elastography is non-painful and non-surgical.
Rapid: It is typically a quick test, which takes about 10-15 minutes to perform.
Safe: It is extremely safe, and no anesthetic or recovery post-examination is necessary.
Convenient: It is a non-radiation test, so there is no danger of exposure to cancer-inducing radiation like with CT scans or X-rays.
Widely Available: Transient elastography (FibroScan) is also offered by most medical facilities around the world and can be employed to assess patients with chronic liver conditions on a regular basis.
4. Clinical Use of Transient Elastography
Fibrosis Staging: It is used most frequently to determine the degree of liver fibrosis. This helps to determine the stage of liver disease:
Stage F0: No fibrosis (normal liver)
Stage F1-F2: Mild to moderate fibrosis
Stage F3: Severe fibrosis (extensive scarring)
Stage F4: Cirrhosis (worst degree of liver damage)
During Disease Progression: In people suffering from chronic liver disease, transient elastography comes in useful for monitoring fibrosis regression or advancement with the passing of time.
Evaluation of Treatment Response: In the case of specific diseases of the liver, like hepatitis C or NAFLD, transient elastography can be utilized to estimate how effective is treatment in lessening liver harm and even reducing the extent of fibrosis.
5. Constraints on Transient Elastography
While transient elastography is an excellent tool to quantify liver stiffness and fibrosis, it is not without some limitations:
Obesity: For very obesity, the technique is less precise as the excess fat within the abdominal compartment can cause a problem with measurement.
Ascites: The accumulation of fluid in the abdomen (ascites), which can occur with advanced liver disease, can also affect the accuracy of the measurements.
Inadequate measurement of liver inflammation: Transient elastography measures only fibrosis (stiffness) but not inflammation or the degree of fatty infiltration (e.g., in NAFLD) directly.
Poor in certain liver diseases: It can produce poor results in patients with some liver diseases, such as acute hepatitis or portal hypertension, as there is an immediate change in liver stiffness.
6. Comparison to Liver Biopsy
Liver biopsy remains the gold standard in the staging and diagnosis of liver fibrosis, but it is invasive and dangerous (bleeding, infection, pain).
Transient elastography is the non-invasive option which is generally less dangerous and easier to perform, but does not replace a biopsy in every instance. Transient elastography may be used for liver fibrosis screening and disease monitoring, and biopsy use in patients with clinical indications necessitating a greater level of evaluation.
7. Other Uses Beyond Liver Disease
Although initially used to assess liver fibrosis, transient elastography has been considered for use in the other organs like the spleen in portal hypertension, but nonetheless, the predominant use remains measuring the condition of the liver.
Summary
Transient elastography is a rapid, easy, and effective tool for the assessment of liver stiffness, which is highly informative in the degree of fibrosis and liver damage. It is widely used in the treatment of chronic liver disease conditions like NAFLD, hepatitis, and cirrhosis and in monitoring the activity of the disease and the response to treatment. It is not without its limitations in some patient populations, such as in patients with very severe obesity or ascites.
Would you like to know more about how transient elastography is different from other imaging methods or its use in a particular liver disease?
Transient elastography (TE), also known by the brand name FibroScan, is a non-invasive imaging test that measures liver stiffness, and it correlates with liver fibrosis. It has been commonly used for diagnosis and monitoring of conditions such as non-alcoholic fatty liver disease (NAFLD), chronic hepatitis, and other liver diseases that result in fibrosis or cirrhosis. Let us know about how transient elastography works and aids in diagnosing liver fibrosis:
1. Principle of Transient Elastography
Transient elastography, or FibroScan, is used to test for liver stiffness (or hardness) by detecting the travel of sound waves through liver tissue. Stiffness is directly related to the amount of fibrosis (scarring).
Elasticity: The normal liver tissue is elastic and soft, and scar tissue of fibrosis hardens the liver.
Shear wave velocity: TE operates by transmitting a burst of low-frequency sound waves (also known as shear waves) through the liver. The speed of the waves is linearly related to liver stiffness: the faster the waves travel, the stiffer the liver and the more fibrosis.
2. Transient Elastography procedure
The procedure is simple, rapid, and painless:
Patient Preparation: Instruct the patient to lie down on their back and lift the right arm such that the right aspect of the abdomen can be accessible. The patient should be without food for accurate results.
Probe Placement: A small ultrasound probe is placed against the skin, typically on the right upper region of the stomach (just below the ribs). The probe emits low-frequency sound waves and measures the return from the liver tissue.
Measurement: The instrument injects a burst of shear waves into the liver and afterwards measures the speed of the generated shear waves in the tissue. The measurement is taken at various locations (approximately 10-15) and an average velocity is derived.
Results: The liver stiffness value is thus reported in units of kilopascals (kPa). The higher values indicate stiffer liver, implying the presence of fibrosis or liver damage.
3. How Liver Stiffness Correlates with Fibrosis
Stiffness value obtained from transient elastography is then utilized to approximate the degree of liver fibrosis. Liver stiffness is usually graded as below:
Normal (no or minimal fibrosis): < 6 kPa
Mild fibrosis: 6–7 kPa
Moderate fibrosis: 7–9 kPa
Severe fibrosis/cirrhosis: > 9 kPa
The cut-off might vary slightly depending on patient population and the disease under evaluation.
4. Advantages of Transient Elastography in Diagnosing Liver Fibrosis
Non-invasive: Unlike a liver biopsy, which requires a needle to harvest liver tissue, transient elastography is completely non-invasive and painless and risk-free.
Fast and simple: The test is normally only 10-15 minutes to carry out.
Reusable: Since it is non-invasive, transient elastography can be used to track changes in liver stiffness over time, and thus healthcare workers can follow the development or reversibility of fibrosis.
Reproducible: It is shown to provide reproducible and consistent results and can be efficiently utilized for regular monitoring.
Non-invasive and no sedation needed: Sedation or anesthesia is not needed in the patient, unlike some imaging tests or liver biopsy.
5. Limitations of Transient Elastography
Transient elastography is a useful tool for diagnosis and quantification of liver fibrosis, but like any measure, it does not exist without limitation:
Obesity: It may be less accurate in individuals with higher body mass index (BMI) because excess fat tissue can interfere with the sound waves. In these cases, the shear waves may not penetrate deeply enough to provide accurate measurements.
Ascites or severe liver congestion: The presence of ascites (fluid in the abdomen) or other conditions affecting liver architecture can affect the results.
Not diagnostic of other liver disease: TE measures liver stiffness, but it cannot definitely diagnose the etiology of the fibrosis (e.g., whether NAFLD, viral hepatitis, alcohol liver disease, etc.). Other testing, including imaging or lab tests, is needed to diagnose underlying liver disease.
Failure to differentiate between cirrhosis stages: Although it can be used to determine the presence of cirrhosis, it may not always be used to differentiate between early cirrhosis and advanced cirrhosis.
6. Clinical Application and Follow-Up
Transient elastography is especially useful in:
Initial Evaluation: It is used to screen for liver fibrosis in patients with liver disease, especially those who have chronic liver diseases such as NAFLD, hepatitis B or C, or alcoholic liver disease.
Tracking Disease Progress: TE is used to track the evolution of liver fibrosis in chronic liver disease with time. It can guide treatment, e.g., starting antiviral therapy in viral hepatitis or dietary changes in fatty liver disease.
Assessment of Treatment Effectiveness: TE is used to assess the effectiveness of interventions (e.g., medication, diet) on reducing fibrosis or preventing cirrhosis progression.
7. Comparison with Other Liver Fibrosis Tests
Liver Biopsy: The gold standard for liver fibrosis diagnosis but is invasive, involves risks (e.g., bleeding, pain), and not feasible for repeated monitoring.
Ultrasound-based elastography (FibroScan): Less precise measure but less expensive than MRI elastography and transient elastography.
MRI Elastography: More sensitive to fibrosis in high BMI or congested liver patients than TE but more expensive and less widely available.
Conclusion
Transient elastography is a convenient, non-invasive tool for diagnosing and following the progression of liver fibrosis and liver disease. It is a quick, accurate, and reproducible assessment of the stiffness of the liver and the severity of the fibrosis, allowing health care professionals to make clinical decisions regarding treatment. It may not be quite as good in certain groups, e.g., in patients with elevated BMI, and further testing may be necessary for full diagnosis.
Would you like more information about how transient elastography is different from other liver tests, or how it is used in some liver diseases?
The Non Alcoholic Fatty Liver Strategy™ eBook by Julissa Clay. The program provided in this eBook is very reasonable and realistic as it neither restricts your diet miserably so that you cannot stick to the changes in diet suggested in it nor wants you to do intense exercises for many hours every week. This program helps in making big changes in your life by following a few easy-to-follow steps.