Published online May 28, 2019. doi: 10.3748/wjg.v25.i20.2503
Peer-review started: October 10, 2018
First decision: November 8, 2018
Revised: November 18, 2018
Accepted: December 27, 2018
Article in press: December 28, 2018
Published online: May 28, 2019
Although it is inevitable to measure shear wave elastography in the same manner among different institutions to utilize the elastography as a standard clinical property, so far there is no unified protocol for this technology.
A degree of liver fibrosis is the most reliable indicator for survival in chronic liver diseases. A standardization of the process to define shear wave elastography should make it valuable not only in a daily clinic but also in various clinical studies by surrogating liver fibrosis.
In this article, it is addressed to clarify from where and how many times shear wave elastography should be measured in the liver to calculate an elastography being representative for the entire liver.
Shear wave elastography was evaluated using two different technologies by placing a region-of-interest with a relatively small size at twelve points scattering throughout the liver to calculate not only a representative value for the entire liver but also a variability of the value throughout the liver. A residual sum-of-square was calculated as a distance from the correlation between the values obtained from two technologies. The limited number of cases was compensated by applying bootstrap values of 1000 iterations in each case.
Both median and distribution of shear wave elastography were significantly different between the right and left lobes. Even after excluding the cases showing the deviation larger than a certain level, the difference of median values was further discrete between lobes. The dispersion of the elastography in the liver was getting larger as the median value was increased toward 1.93 m/sec, then after that the dispersion was getting smaller as the median value was further increased. A residual sum-of-square was increased as the number of measurements in the liver was decreased from twelve points. A sum-of-square was appeared to be significantly larger than that of measurements at twelve sites, when the number of measurement points was decreased to seven.
The difference of shear wave elastography between lobes is not likely due to the difference of dispersion between lobes. The liver fibrosis seems to take place heterogeneously. The heterogeneity should be largest in the middle of the clinical course of chronic liver diseases toward cirrhosis. The variability of median shear wave elastography was increased as the measuring points were decreased.
Shear wave elastography should be measured in both lobes. Heterogeneity of shear wave elastography in the liver would reflect the severity of liver fibrosis. Shear wave elastography should be measured at more than 7 sites in the liver.
Shear wave elastography should be measured at more than seven sites in both lobes. Dispersion of shear wave elastography would provide another insight for the pathogenesis of chronic liver diseases. A recommendation of the number and sites for shear wave elastography measurements in the liver; more than seven points in the both lobes. Dispersion of shear wave elastography in the liver was increased as the lobular reorganization takes place and in turn decreased toward cirrhosis. The evaluation of shear wave elastography, a region-of-interest should be placed eight or more throughout the liver including both lobes. The heterogeneity of fiber accumulation in the liver peaks in the middle of the course of chronic liver diseases from normal to cirrhotic liver. To include the heterogeneity in the evaluation of liver fibrosis using shear wave elastography, the measurements should be performed at more than seven sites in both lobes.The standardization of the procedure in shear wave elastography measurements enables a large-scale multicenter study to achieve multiple evaluations of liver fibrosis in time and space, which leads to clarification of a novel pathogenesis, an efficacy of new drugs, and so on in chronic liver diseases.
In addition to the procedural standardization in shear wave elastography measurements, an industrial standardization of this technology is required for the direct comparison among data that were obtained using machines from different companies and/or implementing a different version of this technology. In parallel with the establishment of a standard procedure in shear wave elastography measurements, a phantom to calibrate an accuracy of shear wave elastography should be explored. Because the significance of shear wave elastography should be determined from the point of clinical outcome, it should be conducted to measure shear wave elastography according to a standard procedure and follow to see the impact of the value on progression/alleviation of the diseases.