Elastography is perhaps the most important breakthrough in the evolution of ultrasonography in the last 15 years.
Elastography is an advanced imaging technology which uses a surface ultrasound for non-invasively assessing the elasticity and stiffness of various tissues in the body. Elasticity of the tissues actually describes the resistance to deformation of a tissue to an applied stress.
In quantitative ultrasound elastography the stress is applied via shear wave propagation generated by ultrasound transducer. The underlying concept in the shear wave speed is related to tissue stiffness and travels faster in stiff tissues and slower in soft tissues.
Liver Elastography is by far the best tool for assessing and evaluating Liver Fibrosis non-invasively. It can evaluate the stiffness of the liver tissue and thus finds out the extension of the liver damage and correctly identifies the stage of fibrosis.
The liver tissue responds to any kind of damage by depositing fibrous tissue and the end results are Liver Cirrhosis and Portal Hypertension, and Hepatic Insufficiency and Hepato-cellular Carcinoma.
Until recently it was the invasive procedure of liver biopsy that was used to do the staging of liver fibrosis.
Now with the advent of Liver Elastography, we can non-invasively stage the liver cirrhosis and can detect the severity of the underlying chronic liver disease and also assess the disease outcome and evaluate the response to therapy.
TE - Transient Elastography or Fibroscan – uses a mechanical wave generated by a special transducer.
ARFI – Acoustic Radiation Force Impulse Imaging
SWE – Shear Wave Elastography or Supersonic Imaging – uses sound waves.
Other newer modalities are also being developed, but TE and ARFI and SWE are the techniques currently in use.
Now with the newer advanced ultrasound machines, Liver Elastography is a totally painless and non-invasive procedure and takes only 10 -15 minutes to perform the scan. Ideally 2 – 4 hours of fasting is required prior to the scanning, and after the procedure, which is purely an OPD procedure, the patient can immediately leave the scanning department and do all his normal activities.
Interpretation of the scans have to be done by an experienced Radiologist who has super specialized in Ultrasound Scanning.
Measurement of Liver Stiffness:
The most commonly used units are Kilopascals (it is actually the measurement of Shear Stiffness) and measurement of the Shear wave speed – (Meter/second).
Normal measurement is less than 5.7 kPa (<1.37m/s)
Mild to Moderate Fibrosis is 5.7 kPa to 15 kPa (1.37m/s to 2.2 m/s)
Severe Fibrosis/Cirrhosis is more than 15 kPa (>2.2m/s)
Elastography techniques can be used to distinguish patient with no or minimal fibrosis (METAVIR STAGE F0 and F1) and differentiate them from those with severe fibrosis or cirrhosis (METAVIR STAGE F3 and F4) with no need to biopsy these groups.
As scar tissue accumulates, the liver loses some of its elasticity and becomes stiffer. Liver elastography involves the use of a surface ultrasound probe that delivers a low frequency pulse or shear wave to a small volume of liver tissue under the rib cage. The transmission of the sound wave is totally painless.
Indications for Liver Elastography
1. Non-alcoholic fatty liver disease.
2. Alcoholic liver disease
3. Non-alcoholic steatohepatitis
4. Chronic Hepatitis B and C|
6. Unspecified Thrombocytopenia
7. Biliary disease (Primary Biliary Cirrhosis & Primary Sclerosing Cholangitis)
8. Persistent Unexplained Abnormal LFTs.
1. Absolutely painless and non-invasive
2. Relatively inexpensive
3. Available easily
4. Both Quantitative and Qualitative assessment of the liver is possible.
5. Long Term follow-up is possible
Detetction of significant liver fibrosis and cirrhosis is important for diagnosing, determining the treatment , prognosis and follow up of chronic liver disease.
Ultrasound Liver Elastography techniques have developed into accurate methods for quantitative non-invasive diagnosis of liver fibrosis.