Different techniques for ultrasound liver elastography

The advent of vibration controlled transient elastography (VCTE or simply TE) with Fibroscan in 2003 the first tool able to noninvasively quantify liver stiffness using ultrasound, thereby providing evidence of liver disease stage can be considered a milestone in hepatology given the limitations of biopsy in terms of sampling and invasiveness. Thresholds for the differentiation of no/mild fibrosis from significant fibrosis, or severe fibrosis or cirrhosis have been provided with TE on the basis of many original works using histology as the reference standard.1,2 From 2009 onwards other new quantitative elastography technologies started to arrive on the market, this time embedded in conventional ultrasound (US) devices. At present almost all ultrasound manufacturers have developed their own liver stiffness quantification modality.2 All share the capacity to assess tissue deformation and measure the speed of shearwaves travelling perpendicular to the axis of an applied force (consisting of ultrasound energy, unlike the Fibroscan which uses the push of a piston). These technologies are collectively called shearwave elastography (SWE), with the two main categories being point SWE (pSWE), which samples a tiny linear portion of tissue (few mm), and bidimensional SWE (2D-SWE), which samples large square areas 14cm2. A more detailed illustration of the various technologies is reported in the EFSUMB guidelines2 and is graphically summarized. Strain elastography is another technology that evaluates tissue stiffness and it is provided by the large majority of manufacturers, since before the advent of SWE. However, it does not provide quantitative measurements of stiffness and did not prove to be as effective as SWE for liver disease: consequently, it has no current role in hepatology.