Original ContributionAcoustic Radiation Force Impulse Elastography of the Liver in Healthy Patients: Test Location, Reference Range and Influence of Gender and Body Mass Index
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.
Section snippets
Methods
This study was approved by the institutional review board of Taipei City Hospital. A total of 106 healthy patients without a history of liver disease and who had undergone a health checkup were prospectively recruited from Renai Branch, Taipei City Hospital, between July and October 2012. All patients gave informed consent for participation in this study. The ARFI test was performed by one experienced doctor under standardized test conditions. Patient laboratory data and ultrasound results
Results
Thirty three of the 68 cases were men and 35 were women. The mean age was 45.4 ± 13.1 y. There was no statistically significant difference in age between the men (45.5 ± 13.7 y) and women (45.4 ± 12.6 y) (p = 0.9793). The mean BMI was 21.9 ± 2.6, and the male patients had a significantly higher BMI than the female patients (23.2 ± 2.1 vs. 20.6 ± 2.4) (p < 0.05) (Table 1).
The median SWV and mean SWV of five valid measurements made at each test location for each subject were calculated and
Discussion
Assessment of liver fibrosis using ARFI elastography has been found to be influenced by many factors such as tissue factors and examination conditions. Its accuracy can be influenced by necro-inflammation (Chen et al. 2012) and serum transaminase levels (Bota et al., 2013, Yoon et al., 2012); the effect of steatosis is controversial (Motosugi et al., 2011, Palmeri et al., 2011, Yoneda et al., 2010). Examination conditions such as food intake (Goertz et al. 2012), deep inspiration (Goertz et al.
Conclusions
The S5/8 supine location was the better test location and was incorporated into the ARFI protocol established in this study. The reference ranges for median and mean SWVs under this protocol were 0.81–1.27 and 0.82–1.27 m/s respectively. Gender and BMI, but not age, were the factors significantly associated with ARFI elastography.
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