What is new in liver elastography

Abstract

In daily practice, many hepatological conditions, such as chronic viral hepatitis, non-alcoholic and alcoholic fatty liver disease (NAFLD and ALD, respectively) need evaluation. This evaluation can be made invasively (by liver biopsy) or non-invasively (by biological tests or by elastographic methods). Elastographic methods can be divided into ultrasound based or magnetic resonance based (MR-Elastography). According to the latest guidelines, (EFSUMB 2017 and WFUMB 2018) ultrasound based elastographic methods can be sub-divided into: Strain Elastography and Shear Wave Elastography (SWE). In hepatological field, SWE is mainly used for liver fibrosis assessment. According to the type of tissue stimulation, SWE can be divided into Transient Elastography (TE) and ARFI technologies (point SWE and 2D-SWE). Transient Elastography (TE) is the oldest elastographic method used in hepatology. Many guidelines and meta-analyses presented its value and limitations (mainly the presence of ascites), including the confounding factors. This method has been proven valuable in HCV and HBV chronic hepatitis, in NAFLD, ALD, post-transplant and in other conditions. The accuracy is increasing with the severity of fibrosis. The New FibroScan system includes a software for spleen stiffness assessment and has a supplementary ultrasound probe for the inspection of the liver, before stiffness evaluation. Point SWE (pSWE) is a quite simple method, working in real time. After the ultrasound examination of the liver, a box of 10/5 mm is placed at more than 1 cm bellow the liver capsule and a button is pressed to measure liver stiffness. The values are expressed in m/s or kPa. The first pSWE system was VTQ (Virtual Touch Quantification) from Siemens, and many papers and meta-analysis proved its good value to predict fibrosis severity in HCV, HBV or NAFLD patients. Later, ElastPQ from Philips was developed and showed a good predictive value in chronic liver disease. Other pSWE techniques were developed by Hitachi, Samsung and other companies. 2D-SWE is a real time elastographic technique, in which liver stiffness is expressed as a colour coded elastogram and also in numeric values. Studies demonstrated that some ultrasound experience is needed for quality measurements. The Aixplorer system from Supersonic Imagine, (SSI) was the first system on the market to use 2D-SWE, and good results of this method were published in several studies and meta-analyses. Other 2D-SWE technologies were developed by GE and Canon, showing good values for clinical practice. Comparative studies were performed in patients with chronic viral hepatitis or NAFLD, evaluating TE, pSWE and 2D-SWE, with liver biopsy as the gold standard. These studies demonstrated that comparable accuracies of al these methods. Studies have been made evaluating TE, pSWE and 2D-SWE as predictors of portal hypertension, but the results are still under discussion regarding pSWE and 2D-SWE. TE has been accepted as a tool to stratify patients at risk for clinically significant portal hypertension. The most recent topic in the field on the non-invasive assessment of liver diseases is the quantification of liver fat. CAP (Controlled Attenuation Parameter) from EchoSens implemented into the FibroScan device, was the first used for liver steatosis quantification. The correlation with histology is quite good (AUROC 0.80-0.85) and CAP is implemented into both the M and XL probes. More recently, other companies such as Hitachi or Canon implemented this type of quantification (attenuation) in their systems (ATT and ATI, respectively), both with interesting results. The same companies included in their latest machines algorithms evaluating the viscosity as a marker of the inflammation in the liver. In this respect, we go now in the direction of a multi-parametric elastographic approach of liver diseases, which quantifies stiffness, steatosis and inflammation. Confounding factors must be known regarding ultrasound based liver elastography to avoid clinical mistakes. In addition, the cut-offs values, which are ultrasound machine specific should be known. Finally, published papers showed the good predictive value of TE, pSWE and 2D-SWE for predicting liver fibrosis severity in daily practice. In conclusion, the body of evidence for ultrasound based elastography is enough strong to recommend this methods for liver diseases assessment. Liver elastography replaced in many cases liver biopsy.