Acoustic Radiation Force Impulse Elastography of the Liver in Healthy Patients: Test Location, Reference Range and Influence of Gender and Body Mass Index

Abstract

The objective of this study was to evaluate the best test location and study factors associated with acoustic radiation force impulse (ARFI) elastography measurements in healthy individuals. When ARFI elastography was performed on 68 healthy patients after controlling for all known test condition factors except segmental location, the median shear wave velocities (SWVs) derived from five valid measurements in the area between S5 and S8 in patients in the supine position had a significantly lower mean and the narrowest 95% confidence interval, followed by those for the S8 supine and S8 semidecubitus locations (p = 0.045). Analysis of mean SWVs revealed similar, although statistically insignificant, findings (p = 0.078). Male patients had significantly higher median SWVs (p = 0.0073) and mean SWVs (p = 0.0043) than female patients. Patients with body mass indexes >22 had significantly lower median SWVs (p = 0.0033) and mean SWVs (p = 0.0008) than those with body mass indexes ≤22. S5/8 supine was the better test location for ARFI. The reference ranges for median and mean SWV were 0.81–1.27 and 0.82–1.27 m/s, respectively. Gender and body mass index, but not age, were the significant factors associated with ARFI SWV values.

Introduction

Acoustic radiation force impulse (ARFI) elastography is a new technology used to detect the propagation speed of shear wave in tissue when a high-intensity acoustic pushing pulse is introduced. The measured shear wave velocity (SWV) is known be linearly correlated with liver tissue stiffness and, therefore, can be used to assess liver fibrosis non-invasively. ARFI elastography allows SWV assessment over a small region of interest (ROI), which can be placed over a region of the liver parenchyma visible on B-mode ultrasound images. It has been found to be well correlated with the changes in fibrosis observed in many chronic liver diseases, particularly hepatitis B and C, and is comparable to transient elastography (TE) as a reliable non-invasive method of liver fibrosis assessment (Chen et al., 2012, Ferraioli et al., 2012, Kuroda et al., 2010, Takahashi et al., 2010, Toshima et al., 2011, Yoneda et al., 2010). Unlike TE, ARFI elastography has no limitations in patients with ascites and its success rate is higher (Boursier et al., 2010, Friedrich-Rust et al., 2009, Fierbinteanu-Braticevici et al., 2009, Piscaglia et al., 2011). However, without a standard protocol, studies of normal patients produce discrepant results, with the mean values of healthy patients varying from 0.97 to 1.56 m/s, probably because of the variation in the test protocols used in different studies (Crespo et al., 2012, D’Onofrio et al., 2013, Karlas et al., 2011, Madhok et al., 2013, Popescu et al., 2011, Rizzo et al., 2011, Son et al., 2012, Sporea et al., 2011). Examination conditions such as food intake, inspiration or expiration, body position and depth and angle of the ROI have all been found to be factors that may influence the test results (Goertz et al., 2012, Jaffer et al., 2012, Karlas et al., 2011). Interlobe differences have also been reported (Karlas et al., 2011, Toshima et al., 2011). Therefore, it is important to establish the test protocol of ARFI elastography with defined test conditions and test location. The aims of this study were to determine the better segmental test location for the test, to establish an ARFI protocol with this test location included, to define the reference range for ARFI elastography and to analyze factors (gender, age and body mass index) associated with ARFI shear wave velocity.