Ultrasound elastographic techniques in focal liver lesions

Abstract

Elastographic techniques are new ultrasound-based imaging techniques developed to estimate tissue deformability/stiffness. Several ultrasound elastographic approaches have been developed, such as static elastography, transient elastography and acoustic radiation force imaging methods, which include point shear wave and shear wave imaging elastography. The application of these methods in clinical practice aims at estimating the mechanical tissues properties. One of the main settings for the application of these tools has been liver stiffness assessment in chronic liver disease, which has been studied mainly using transient elastography. Another field of application for these techniques is the assessment of focal lesions, detected by ultrasound in organs such as pancreas, prostate, breast, thyroid, lymph nodes. Considering the frequency and importance of the detection of focal liver lesions through routine ultrasound, some studies have also aimed to assess the role that elestography can play in studying the stiffness of different types of liver lesions, in order to predict their nature and thus offer valuable non-invasive methods for the diagnosis of liver masses.

Keywords: Acoustic radiation force imaging; Elastographic techniques; Focal liver lesions; Shear wave imaging; Transient elastography.

Figure 1

Image of a focal liver lesion obtained by static real-time elastography: The focal liver lesion appears hyperechoic at ultrasound image (left) and stiffer (predominantly blue) in the elasticity image. At histology the lesion revealed to be a hepatocellular carcinoma.

Figure 2

Transient elastography uses a low-frequency pulsed excitation to generate shear waves in the tissue, with the velocity of the shear wave - established to be related to tissue stiffness - to be measured with an ultrasound pulse-echo technique and used to calculate the elasticity.

Figure 3

Shear wave ultrasound elastography allows to gather information on the tissue stiffness of both the parenchyma and focal liver lesion, obtaining a quantitative assessment.