Quantitative Elastography Methods in Liver Disease: Current Evidence and Future Directions

Abstract

Chronic liver diseases often result in the development of liver fibrosis and ultimately, cirrhosis. Treatment strategies and prognosis differ greatly depending on the severity of liver fibrosis, thus liver fibrosis staging is clinically relevant. Traditionally, liver biopsy has been the method of choice for fibrosis evaluation. Because of liver biopsy limitations, noninvasive methods have become a key research interest in the field. Elastography enables the noninvasive measurement of tissue mechanical properties through observation of shear-wave propagation in the tissue of interest. Increasing fibrosis stage is associated with increased liver stiffness, providing a discriminatory feature that can be exploited by elastographic methods. Ultrasonographic (US) and magnetic resonance (MR) imaging elastographic methods are commercially available, each with their respective strengths and limitations. Here, the authors review the technical basis, acquisition techniques, and results and limitations of US- and MR-based elastography techniques. Diagnostic performance in the most common etiologies of chronic liver disease will be presented. Reliability, reproducibility, failure rate, and emerging advances will be discussed. ^© RSNA, 2018 Online supplemental material is available for this article.

Figure 1:

Illustrations of US elastography techniques, including TE (FibroScan, Echosens), pSWE (Virtual Touch Quantification, Siemens Acuson S2000), 2D SWE (Aixplorer, Supersonic Imagine), and MR elastography. Sampling area for each method is depicted by enclosed green area. TE and pSWE have a fixed sampling area size, though pSWE allows the depth and location to be chosen. Two-dimensional SWE has the ability of pSWE sampling area placement with the additional ability to change the size. MR elastography offers (near) full organ coverage. Corresponding example images for each method are also shown. TE = transient elastography, pSWE = point shear-wave elastography, 2D SWE = two-dimensional shear-wave elastography.

Figure 2:

Transient elastography images. Left: image in a 39-year-old woman with chronic hepatitis C virus infection with no fibrosis (stage F0) (liver stiffness, 3.2 kPa; M probe). Middle: image in a 59-year-old man with chronic hepatitis B virus infection with stage F2 fibrosis (liver stiffness, 8.7 kPa; M probe), Right: Image in a 57-year-old man with nonalcoholic fatty liver disease with cirrhosis (liver stiffness, 27.0 kPa; XL probe). Liver stiffness measurement (Young modulus, median value of 10 measurements), interquartile range, and median value percentage are automatically calculated. An elastographic image (red box) shows axial displacement in terms of depth (y-axis) and time (x-axis). In stiffer tissues, the shear wave propagates more quickly and produces a steeper time-depth gradient (arrows).

Figure 3:

A, Successful and, B, unsuccessful point shear-wave elastographic acquisition (Siemens Acuson S3000) in a 58-year-old man with chronic hepatitis C virus infection and stage F2 liver fibrosis. Unsuccessful measurement (displaying as X.XX m/s) related to poor breath hold. In the successful measurement, wave speed was measured at 1.10 m/sec.

Figure 4:

Images obtained with the same system (Siemens Acuson S3000) in a 50-year-old woman with grade 2 steatosis without fibrosis. A, Point shear-wave elastographic image demonstrates placement of fixed-size region of interest in the right hepatic lobe, with measured wave speed of 1.17 m/sec. B, During the same examination, two-dimensional shear-wave elastographic image shows placement of larger size region of interest in the same area, with color elasticity map, and measured wave speed of 1.33 m/sec with interquartile range of 0.21 m/sec.

Figure 5:

MR elastography performed by using a two-dimensional gradient-recalled-echo sequence and a two-dimensional inversion algorithm in a 52-year-old woman with advanced liver fibrosis (stage F3) secondary to nonalcoholic steatohepatitis. A, Transverse magnitude image with intravoxel phase dispersion (arrows) present under the actuator (which is not visible on MR images). B, Transverse image with waves visible in liver parenchyma. C, Transverse colorized wave image shows wave propagation through liver parenchyma. D, Transverse gray-scale elastogram. E, Transverse colorized elastogram (0–8-kPa scale). F, Transverse colorized elastogram (0–8-kPa scale) with 95% confidence grid overlaid highlighting areas of reliable liver stiffness measurement. Liver stiffness was increased (5.3 KPa).

Figure 6:

Transverse T2-weighted half-Fourier acquisition single-shot turbo spin-echo, or HASTE, anatomic images (top) and transverse MR elastograms (bottom) depict increasing liver stiffness with increasing fibrosis in patients with chronic hepatitis C virus infection: stage F1 in a 51-year-old man, stage F2 in a 67-year-old man, stage F3 in a 46-year-old man, and stage F4 in a 65-year-old woman. Anatomic images depict no significant liver nodularity in patients with stage F3–F4 fibrosis, while MR elastograms reveal increasing stiffness (yellow and red colored areas).

Figure 7:

Top row, images in 43-year-old woman with nonalcoholic steatohepatitis and advanced fibrosis (stage F3) at liver biopsy. A, Transverse PDFF image demonstrates mild steatosis (PDFF, 14.6%). B, Transverse wave image obtained with MR elastography demonstrates increased wavelength (thicker waves) in liver parenchyma. C, Transverse elastogram demonstrates increased liver stiffness (4.33 kPa). Bottom row, images in a 29-year-old woman with nonalcoholic fatty liver disease with no fibrosis (stage F0) at liver biopsy. D, Transverse PDFF image demonstrates mild steatosis (PDFF, 9.2%). E, Transverse wave image obtained with MR elastography demonstrates short wavelengths in the liver (thinner waves) parenchyma. F, Transverse elastogram demonstrates normal liver stiffness (2.22 kPa). PDFF = proton density fat fraction.

Figure 8:

A, Transverse T2-weighted half-Fourier acquisition single-shot turbo spin-echo, or HASTE, MR anatomic image with arrows indicating actuator position and, B, transverse stiffness map in a 27-year-old healthy woman with normal liver stiffness (2.1 kPa) and spleen stiffness measured at 4.3kPa. C, Transverse anatomic image with arrows indicating actuator position and, D, transverse stiffness map in a 61-year-old female patient with cirrhosis (secondary to chronic hepatitis C virus infection) and clinically significant portal hypertension (hepatic venous pressure gradient of 15 mmHg) demonstrate elevated liver stiffness (7.5 kPa) and spleen stiffness (9.9 kPa).

Figure 9:

Transverse T2-weighted half-Fourier acquisition single-shot turbo spin-echo, or HASTE, anatomic image (left) and transverse MR elastogram (right) in a 59-year-old man with chronic hepatitis C virus infection and infiltrative hepatocellular carcinoma in right hepatic lobe (arrows). MR elastography demonstrates increased stiffness (7.7 kPa) compared with background liver parenchyma (3.2 kPa). Another hepatocellular carcinoma nodule is present in left lateral hepatic lobe (arrowheads), also demonstrating increased stiffness.

Figure 10:

Images in a 61-year-old man with cirrhosis secondary to chronic hepatitis C virus infection and secondary hemosiderosis causing failure of two-dimensional gradient-recalled-echo (GRE) MR elastography (MRE) at 1.5 T. The shortened liver T2* (4.7 msec) due to iron deposition causes low signal-to-noise ratio, with disorganized wave propagation pattern and no areas of reliable stiffness measurement. Two-dimensional echo-planar imaging (EPI) sequence performed during the same MR imaging examination is less sensitive to T2* effects, allowing successful wave propagation and liver stiffness measurement (5.6 kPa).

Figure 11:

Images in a 57-year-old man with decompensated cirrhosis (secondary to chronic hepatitis C virus infection) and large ascites causing two-dimensional gradient-recalled-echo MR elastography failure. A, Transverse T2-weighted half-Fourier acquisition single-shot turbo spin-echo, or HASTE, image shows cirrhotic liver (liver contour outlined in white) and large ascites (arrows). B, Transverse wave image shows propagation in subcutaneous fat and fluid but disrupted waves in liver parenchyma, resulting in no reliable areas of stiffness measurement on, C, transverse elastogram.