Liver fibrosis assessment: MR and US elastography

Abstract

Elastography has emerged as a preferred non-invasive imaging technique for the clinical assessment of liver fibrosis. Elastography methods provide liver stiffness measurement (LSM) as a surrogate quantitative biomarker for fibrosis burden in chronic liver disease (CLD). Elastography can be performed either with ultrasound or MRI. Currently available ultrasound-based methods include strain elastography, two-dimensional shear wave elastography (2D-SWE), point shear wave elastography (pSWE), and vibration-controlled transient elastography (VCTE). MR Elastography (MRE) is widely available as two-dimensional gradient echo MRE (2D-GRE-MRE) technique. US-based methods provide estimated Young's modulus (eYM) and MRE provides magnitude of the complex shear modulus. MRE and ultrasound methods have proven to be accurate methods for detection of advanced liver fibrosis and cirrhosis. Other clinical applications of elastography include liver decompensation prediction, and differentiation of non-alcoholic steatohepatitis (NASH) from simple steatosis (SS). In this review, we briefly describe the different elastography methods, discuss current clinical applications, and provide an overview of advances in the field of liver elastography.

Keywords: Chronic liver disease; Fibrosis staging; Liver stiffness; Non-alcoholic steatohepatitis; Shear stiffness.

Fig. 1

MRE stiffness maps from different subjects. Color scale from 0 to 8 kilopascals (kPa) on the right. Normal liver stiffness of 1.8 kPa in a liver donor (a). Patients with chronic hepatitis C with biopsy-proven liver fibrosis stage 0 (b), stage 1 (c), stage 2 (d), stage 3 (b, e), and stage 4 or cirrhosis (f) with liver stiffness measurements of 2.6 kPa, 3.0 kPa, 3.6 kPa, 4.4kpa, and 8.1 kPa, respectively. The dotted lines represent the outline of the liver copy pasted from magnitude images (not shown)

Fig. 2

Utility of MRE in NAFLD patients. Top row images from a patient with biopsy-proven simple steatosis and bottom row images are from another patient with biopsy-proven steatohepatitis only. In phase (a, d) and opposed phase (b, d) and stiffness maps (c, f) from MRE. In patient with simple steatosis, the estimated fat signal fraction is 36% and liver stiffness measurement was 1.9 kPa (normal < 2.5 kPa). In the patient with steatohepatitis only the estimated fat signal fraction was 24% and liver stiffness measurement was 3.4 kPa

Fig. 3

MRE stiffness maps of a patient with chronic hepatitis C at baseline (a) and follow-up (b) after 6 years of successful antiviral therapy and sustained viral response. Liver biopsy performed before baseline MRE showed stage 1–2 fibrosis. The baseline liver stiffness was 3.5 kPa and improved to 2.7 kPa at follow-up. Patient is currently followed up with MRE

Fig. 4

Poor ROI color fill-in in an elastogram

Fig. 5

A- and TM modes help operators to find the ideal liver location for stiffness measurements

Fig. 6

Internal quality assessment process for ROI. a The software does not suggest this location (red ROI in inset) suitable for assessment. b The software suggests this location (yellow ROI in inset) suitable for assessment

Fig. 7

Shear wave elastography (SWE) with confidence map. Some vendors provide additional quality metrics to assist the operators to acquire high quality SWE images. The homogeneous, yellow color area on the left side of the image indicates high confidence