What is Hepatic Elastography?
Hepatic Elastography is a diagnostic imaging test that allows the assessment of liver elasticity. It is a non-invasive method for detecting the presence of fibrosis, which has been progressively replacing liver biopsy, the latter being an invasive technique with non-negligible risks.
Transient elastography, also known as FIBROSCAN, has been the most widely used method for measuring liver fibrosis until a few years ago. However, this system measures fibrosis “blindly”, i.e. without a visual control of the liver and has very important limitations in cases of obesity and ascites.
For this reason, elastography incorporated into ultrasound equipment has been gaining ground in recent years, since it allows liver ultrasound and fibrosis measurement to be performed at the same time. The fact of being able to visually control the areas where the elastographic measurements are taken makes the data obtained more reliable and allows the study to be more representative since the liver can be “mapped” to a greater extent. In addition to these advantages, the limitations described for Fibroscan (obesity and ascites) can be overcome.
What does it consist of?
Ultrasound-mediated liver elastography does not differ technically from conventional ultrasound. Its rationale could be summarized as follows: By means of the emission of a low-frequency mechanical pulse by means of an ultrasound probe, the spread in the tissue and the elasticity or deformation it presents is assessed. It is understood that the greater the elasticity, the lesser the presence of fibrosis.
These parameters are expressed as a numerical value. After a certain number of measurements in different hepatic areas, the median of the values obtained is obtained as the final value, which will confirm or not the presence of fibrosis. In addition, a classification is established in degrees from less to more fibrosis, according to ranges of values.
There are several types of elastography:
- Transitional elastography or Fibroscan, which is not ultrasound-mediated. On the other hand, ultrasound-mediated elastography, also known as ARFI (acoustic Radiation Force Impulse), which includes point Shear Wave Elastography (pSWE).
- two-dimensional shear wave elastography (2D-SWE).
- ARFI-type ultrasound-mediated elastography has the best correlation with anatomopathological studies (biopsy as the reference method) for determining and grading liver fibrosis.
Why is it performed?
All chronic liver disease (fatty liver disease, viral hepatitis, alcoholic hepatitis, autoimmune hepatitis, autoimmune cholangitis, deposit diseases and any pathology that generates chronic liver damage) requires periodic clinical, analytical and ultrasound monitoring.
The reason for this is the early detection of complications and poor evolution of the disease in question. Liver ultrasound, in expert hands, is capable of diagnosing with high precision advanced stages of chronic liver disease, such as compensated or decompensated cirrhosis. However, it loses accuracy in the detection of fibrosis in early stages, so in these cases elastography plays a fundamental role.
Elastography makes it possible to detect fibrosis in early and intermediate stages, before reaching a situation of advanced fibrosis or cirrhosis. This is especially important because it has a clear impact on the prognosis of the disease. Early detection of fibrosis at early stages allows treatment to be initiated, changed or intensified, thus improving the prognosis.
Preparation required
The only preparation required is a minimum fasting of 6 hours. The patient’s cooperation with simple respiratory maneuvers is required. The time required varies between 10 and 30 minutes, although in general about 15 minutes is usually sufficient.
What does the test feel like?
The test is performed in the same way as a conventional ultrasound, so it is painless and harmless. The patient lies on the table in the supine (“face up”) position, with the right arm flexed and placed behind the head. The patient is not subjected to any type of radiation, nor is there any interference with prostheses or metallic devices they may be wearing.
Meanings of abnormal results
The results are classified into the following grades:
- F0-F1: absence of fibrosis.
- F2: mild fibrosis
- F3: intermediate grade clinically significant fibrosis
- F4: advanced fibrosis and/or cirrhosis Each category or grade is defined with a range of values.
This range varies according to the type of elastography performed, so the values are not comparable or superimposable between different elastographic techniques, but the category or grade in which it is classified is. However, the result should always be correlated with the patient’s clinical history. There are situations in which falsely elevated values or overestimation of fibrosis can be obtained. These situations are congestive heart failure or stasis liver, hepatic tumor infiltration or lack of fasting due to postprandial hyperemia.
Advances
Technological development in the field of ultrasound and, specifically, of hepatic elastography has been progressive since the commercialization of Fibroscan. Advances are continuous, as the major ultrasound scanner manufacturers have developed their own elastography software, as well as multicenter studies that allow establishing ranges of values for the grading of liver fibrosis by etiology.
Currently, the latest is the 2D-SWE elastography system that displays color maps according to stiffness ranges and confidence maps, all aimed at improving the accuracy and manageability of the technique.
Liver elastography is a noninvasive method for the diagnosis of fibrosis. Quantification of fibrosis by elastography imaging methods allows accurate diagnosis of clinically significant fibrosis and cirrhosis. Different elastography methods are available.
The pioneering and most studied method has been transitional elastography or Fibroscan. In recent years, the different ultrasound-mediated elastography methods are displacing Fibroscan, due to its integration in conventional ultrasound equipment, the possibility of selecting the area of analysis and fewer technical limitations in obese patients or those with ascites.
In chronic liver disease, early detection of fibrosis modifies treatment and improves prognosis.
This definition has been written by Dr. Francisco Javier Álvarez Higueras, specialist in Digestive System.