Ultrasound Shear Wave Elastography for Liver Disease. A Critical Appraisal of the Many Actors on the Stage

Abstract

In the last 12 - 18 months nearly all ultrasound manufacturers have arrived to implement ultrasound shear wave elastography modality in their equipment for the assessment of chronic liver disease; the few remaining players are expected to follow in 2016.When all manufacturers rush to a new technology at the same time, it is evident that the clinical demand for this information is of utmost value. Around 1990, there was similar demand for color Doppler ultrasound; high demand for contrast-enhanced ultrasonography was evident at the beginning of this century, and around 2010 demand increased for strain elastography. However, some issues regarding the new shear wave ultrasound technologies must be noted to avoid misuse of the resulting information for clinical decisions. As new articles are expected to appear in 2016 reporting the findings of the new technologies from various companies, we felt that the beginning of this year was the right time to present an appraisal of these issues. We likewise expect that in the meantime EFSUMB will release a new update of the existing guidelines 1 2.The first ultrasound elastography method became available 13 years ago in the form of transient elastography with Fibroscan(®) 3. It was the first technique providing non-invasive quantitive information about the stiffness of the liver and hence regarding the amount of fibrosis in chronic liver disease 3. The innovation was enormous, since a non-invasive modality was finally available to provide findings otherwise achievable only by liver biopsy. In fact, prior to ultrasound elastography, a combination of conventional and Doppler ultrasound parameters were utilized to inform the physician about the presence of cirrhosis and portal hypertension 4. However, skilled operators were required, reproducibility and diagnostic accuracy were suboptimal, and it was not possible to differentiate the pre-cirrhotic stages of fibrosis. All these limitations were substantially improved by transient elastography, performed with Fibroscan(®), a technology dedicated exclusively to liver elastography. Since then, more than 1300 articles dealing with transient elastography have been listed in PubMed, some describing results with more than 10,000 patients 5. The technique has been tested in nearly all liver disease etiologies, with histology as the reference standard. Meta-analysis of data, available in many etiologies 6, showed good performance and reproducibility as well as some situations limiting reliability 5. Thresholds for the different fibrosis stages (F0 to F4) have been provided by many large-scale studies utilizing histology as the reference standard 7. Transient elastography tracks the velocity of shear waves generated by the gentle hit of a piston on the skin, with the resulting compression wave traveling in the liver along its longitudinal axis. The measurement is made in a 4 cm long section of the liver, thus able to average slightly inhomogeneous fibrotic deposition.In 2008 a new modality became available, Acoustic Radiation Force Impulse ...

Intra- and inter-observer variation and accuracy using different shear wave elastography methods to assess circumscribed objects – a phantom study.

“…The shear wave quality indicator -Propagation (arrival time contour) mode (feature only available with the product of Toshiba Medical Systems, Minato, Japan) -should provide real-time feedback and optimize placement of the vROI -which still awaits validation. Quantitative information of tissue stiffness can be obtained in this shear wave speed imaging by captur- ing the transverse shear waves propagation induced by the displacement of tissues under the excitation of ultrasound acoustic push pulses [25]. Tissue excitation in 2D-SWE is similar to that in pSWE, the wave speed is calculated using wave-peak detection and a time-of-flight algorithm.…”

Non-Invasive Assessment of Liver Fibrosis in a Rat Model: Comparison of Shear Wave Elastography with Serologic Tests

“…TE has been tested in nearly all liver disease etiologies and consistently showed good reproducibility and diagnostic performance. Until now, there are more than 600 articles published in PubMed that have studied transient elastography (23). Reference standard of thresholds for different fibrosis stages can also be available in guidelines of the World Federation for Ultrasound in Medicine and Biology.…”

Advances in the diagnosis and treatment of liver fibrosis

“…[38,40] MRE MRE adopts a phase contrast imaging method which depends on mechanical wave propagation to assess the degree of liver stiffness.…”