Tag Archives: Liver

Shear Wave Elastography and Diffuse Liver Disease

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Diffuse liver disease is a worldwide problem. The causes are several, with non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease, and viral B or C hepatitis being the most frequent. No matter what the cause is, the chronic inflammation of the liver and the cellular death lead to liver tissue scarring, namely liver fibrosis, that may progress to cirrhosis with its complications.

Staging liver fibrosis is important for the management and prognosis of diffuse liver disease. For decades, liver biopsy has been the reference standard for the staging of liver fibrosis.

Shear wave elastography (SWE) is a method able to assess the tissue stiffness by applying a mechanical stress that induces the generation of shear waves, which then propagates into the tissue with a speed that is proportional to the stiffness of the tissue. The shear waves are generated by a body-surface compression, as in transient elastography (TE), or by the push-pulse of a focused ultrasound beam, as in acoustic radiation force impulse (ARFI) techniques.

The speed of the shear waves is related to the stiffness: they travel faster in stiffer tissue. Using a formula and making some assumptions, it is possible to convert the speed into units of stiffness, ie kilopascals.

A fibrotic tissue is harder (stiffer) than a normal tissue, and an increase of fibrosis is coupled with an increase of the stiffness. Therefore, there is a close positive relationship between fibrosis and stiffness.

TE is an SWE technique performed with the FibroScan system (Echosens). This system has a probe with a tip at the end and a button on the lateral part of it. By pushing the button, the tip compresses the body surface and this deformation propagates into the liver as shear waves. An ultrasound beam tracks the shear wave speed and sends information back to the software of the system. The final reading is in kilopascals. The FibroScan quantifies the stiffness but doesn’t assess the morphology of the liver.

The ARFI techniques are implemented in ultrasound systems that are used for other diagnostic purposes when a patient with diffuse liver disease is evaluated. In fact, using an ultrasound system, it is possible to study the organ’s morphology with B-mode, the hemodynamics with Doppler, and to characterize focal liver lesions with contrast agents. ARFI techniques make use of the energy of the ultrasound beam to generate the shear waves whose speed propagation is assessed in m/s: higher the speed stiffer the tissue.

ARFI techniques include point shear wave elastography (pSWE) and two-dimensional shear wave elastography (2D-SWE). pSWE measures the stiffness in a small and fixed region of interest whereas with 2D-SWE the stiffness is obtained over a large field of view and a color-coded image, from which the stiffness value is gotten, is displayed on the monitor of the ultrasound system. The shear wave speed can be converted into kilopascals; the ultrasound systems generally provide both speed values in m/s and stiffness values in kilopascals.

The stress is made directly into the liver; therefore, the examination can be performed also in patients with ascites.

All the published studies have shown that the ARFI techniques have accuracy similar to or higher than FibroScan for the staging of liver fibrosis. Over the last years, the assessment of liver stiffness with SWE techniques, either TE or ARFI, has increasingly been used as a means to noninvasively staging liver fibrosis. Currently, guidelines have accepted that SWE techniques can safely replace liver biopsy in several clinical scenarios. SWE can safely be used also in children. It is feasible in children of all ages and has many pediatric applications in the setting of chronic liver disease.

Bibliography

  • Barr RG, Wilson SR, Rubens D, Garcia-Tsao G, Ferraioli G. Update to the Society of Radiologists in Ultrasound Liver Elastography Consensus Statement. Radiology 2020; 296:263–74.
  • Ferraioli G, Wong VW, Castera L, Berzigotti A, Sporea I, Dietrich CF, Choi BI, Wilson SR, Kudo M, Barr RG. Liver Ultrasound Elastography: An Update to the WFUMB guidelines and recommendations. U Med Biol 2018; 44:2419–2440.
  • Ferraioli G. Review of liver elastography guidelines. J Ultrasound Med 2019; 38:9–14.
  • Ferraioli G, Barr RG, Dillman JR. Elastography for pediatric chronic liver disease: a review and expert opinion. J Ultrasound Med 2020; doi: 10.1002/jum.15482

Giovanna Ferraioli, MD, FAIUM, is a researcher at Medical School University of Pavia, Italy. She’s the lead author of WFUMB guidelines on liver elastography, co-author of the SRU consensus, and of several international guidelines on elastography.

Interested in learning more? Check out the following posts from the Scan:

Should You Include CEUS and Elastography in Your Liver US Practice?

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Today, the liver is regarded with high importance by our clinical colleagues. The obesity epidemic, with its considerable impact in North America, is associated with severe metabolic disturbances including nonalcoholic fatty liver disease (NAFLD). Further, liver cancer is the only solid organ cancer with an increasing incidence in North America. Where do we as ultrasonographers fit into the imaging scheme to most appropriately deal with these new challenges?

The liver is the largest organ in the body, and certainly the most easily accessed on an abdominal ultrasound (US). It has been the focus of countless publications since the introduction of abdominal ultrasound many decades ago. Exquisite resolution allows for excellent detailed liver evaluation allowing US to play an active role in the study of both focal and diffuse liver disease. Focal liver masses are often incidentally detected on US examinations performed for other reasons and on scans performed on symptomatic patients. Abdominal pain, elevated liver function tests, and nonspecific systemic symptoms may all be associated with liver disease. The introduction of color Doppler to abdominal US scanners many years ago elevated the role of US by allowing for improved capability of US to participate in assessment of the hemodynamic function of the liver as well.

malignant tumor ceus

The well-recognized value of abdominal US, including detailed morphologic liver assessment, has made this examination the most frequent study performed in diagnostic imaging departments worldwide. However, in recent years, US has been relegated to an inferior status relative to CT and MR scan, as their use of intravenous contrast agents has made them the cornerstone modalities for virtually all imaging related to the presence of focal liver masses. As we now live in an era of noninvasive diagnosis of focal liver disease, greyscale US has fallen out of favor, as it is nonspecific for liver mass diagnosis. While US is the recommended modality for surveillance scans in those at risk for development of hepatocellular carcinoma, today, all identified nodules are then investigated further with contrast-enhanced CT and/or MR scan.

In the more recent past, US has been augmented by 2 incredible noninvasive biomarkers: elastography, which measures tissue stiffness, and contrast-enhanced ultrasound, which shows perfusion to the microvascular level for the first time possible with US. These noninvasive additions are invaluable and their adoption in routine US practices may allow the reemergence of US as a major player in the field of liver imaging.

Most conventional US machines today are equipped with the capability to perform elastography, especially with point shear wave techniques (pSWE). In pSWE, an ARFI pulse is used to generate shear waves in the liver in a small (approximately 1 cm3) ROI. B mode imaging is used to monitor the displacement of liver tissue due to the shear waves. From the displacements monitored over time at different locations from the ARFI pulse, the shear wave speed is calculated in meters per second, with higher velocities associating with increased tissue stiffness. The accuracy for the determination of liver fibrosis and cirrhosis with pSWE as compared with gold standard liver biopsy is now indisputable. Because of the great significance of liver fibrosis secondary to fatty liver and the obesity epidemic, the development of this technique as a routinely available study is essential. Because of the frequent selection of US as the first test chosen for any patient suspect to have undiagnosed diffuse liver disease, the opportunity for elastography to be included with the diagnostic morphologic US test should be developed as a routine.

Contrast-enhanced US (CEUS), similarly, is available on most currently available mid- and high-range US systems, allowing for nondestructive low MI techniques to image tumor and liver vascularity following the injection of microbubble contrast agents for US. This allows for a similar algorithmic approach to contrast-enhanced CT and MR scan for noninvasive diagnosis of focal liver masses. CEUS additionally offers unique imaging benefits that include no requirement for ionizing radiation and also imaging without risk of nephrotixity, invaluable in the many patients who present for imaging with high creatinine, preventing injection of both CT and MR contrast agents.

Incorporation of pSWE and CEUS into standard liver US in patients with suspect diffuse or focal liver disease is a cost-effective and highly appropriate consideration as this is readily available, performed without ionizing radiation, and at a considerable cost saving over all other choices.

Can you diagnose a hepatocellular carcinoma or other liver tumor with CEUS?  And, can you determine if a liver is cirrhotic or not?  With the addition of pSWE and CEUS to your liver US capability, yes, you can.

What is your experience with treating liver disease? What aspect is most difficult for you? What other area do you think would benefit from the addition of CEUS? Comment below or let us know on Twitter: @AIUM_Ultrasound.

Stephanie R Wilson is a Clinical Professor at the University of Calgary.