Vibration-controlled Transient Elastography

A Practical Approach to the Noninvasive Assessment of Liver Fibrosis

Elliot B. Tapper; Nezam H. Afdhal

Disclosures

Curr Opin Gastroenterol. 2015;31(3):192-198. 

In This Article

What Is Vibration-controlled Transient Elastography?

Given the risk, cost and sampling error associated with liver biopsy clinicians have long sought for alternatives.[7] VCTE is a well tolerated, reliable and inexpensive alternative to liver biopsy. The patient's experience of VCTE is not unlike receiving a liver ultrasound. The device and a sample read-out are described in Fig. 1. A technician places a handheld probe with conduction gel in the intercostal space overlaying the right hepatic lobe. The probe emits a 50 mHz shear wave into the liver and the velocity of that shear wave is measured with a transducer at the tip of the probe. The velocity of returning shear waves is measured at a depth determined by the specific probe used. Though it is often referred to as 'transient-elastography', we specify that it is vibration-controlled based on the emission of the shear wave from the probe, rather than another technique (e.g. sound wave). Given that chest wall thickness varies, it is a critical determinant of VCTE success and should be addressed with appropriate probe choice.[8–12] The 'M' probe measures shear-wave velocity at a depth of 25–65 mm, the 'XL' probe at 35–75 mm.[13,14] This velocity is converted mathematically into a liver stiffness measurement (LSM) rendered in kiloPascals (kPa) using Hook's law. In practice, VCTE provides the median LSM value (with interquartile range) from a minimum of 10 successful measurements. LSM does not absolutely 'stage' fibrosis as would a biopsy. Higher values, rather, provide a risk estimate of advanced liver disease that correlates well with histology. Unlike blood-based noninvasive tests of liver fibrosis, the LSM is immediately available to inform clinical decisions with the patient.

Figure 1.

The FibroScan VCTE device and its readout. In this figure, the entire device is depicted in (a). The probes are shown in (b), the standard 'M' probe on top, the 'XL' probe on the bottom. The tip of the probe is an ultrasound transducer. The basic readout of the FibroScan examination is shown in (c). In this picture, the mechanical vibration-induced shear wave is followed on two axes (depth and time) as it propagates through the liver. The angle of the shear-wave face reflects its speed, faster waves are more vertical. Faster waves reflect stiffer livers. As such, it is this speed that is mathematically interpreted as liver stiffness. Figure published with permission from FibroScan, Sandhill Scientific Inc. VCTE, vibration-controlled transient elastography.

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