Liver stiffness measurement

Simultaneously, TE, ARFI, and SSI were conducted for LSM after at least 2-hour fast and within 1 month of percutaneous liver biopsy.

Transient elastography (TE, Echosens, Paris, France) was performed with the Fibroscan^® system using the M probe. The examinations were carried out by a well-trained radiologic technician (with an experience of more than 1,000 cases of TE LSM) blinded to ARFI and SSI results and histological data. As previously described [11, 20], poorly reliable or unreliable data were defined as an interquartile range (IQR) per median of LSM (IQR/M) > 0.3 with a median LSM ≥ 7.1 kPa, and those unreliable results were excluded from analysis.

The ARFI imaging was conducted by two experienced radiologists (H.W. with 13 year-experience for abdominal ultrasound; M.S.L. with 10 year-experience for abdominal ultrasound) blinded to TE and SSI results and histological data, using Acuson S2000 (Siemens AG, Erlangen, Germany). Since the inter-observer agreement of ARFI imaging proved highly reliable (0.927–0.958) in our center [15], repeat measurements between the two radiologists were not performed. The patients were required to be supine with their right arms raised overhead to increase the intercostal acoustic window. An ARFI-integrated convex probe (5C1) was positioned in the intercostal space perpendicular to the liver capsule to properly visualize the right lobe of the liver in the optimal acoustic window. The 10 × 5 mm ROI cursor was positioned in the area of liver parenchyma deeper than 2 cm from the liver capsule and free from large blood vessels, reverberation artifacts, and acoustic shadowing. Ten valid measurements at the same area were obtained from each patient during their late expiratory phases with breath-hold and the median value expressed in meters per second (m/s) was regarded as a representative value of liver stiffness. When an IQR/M was > 0.3 if the LSM was > 1.5 m/s, the measurement was considered unreliable [21].

The SSI (AiXplorer, Aix-en-province, France) with an SSI integrated convex probe (SC6-1) system was used for measuring shear-wave speed. One of the authors (W.K. with 12-year experience of liver ultrasound) who were not involved in performing ARFI measurement and were blinded to TE and ARFI results and histological data implemented SSI. Patient position, probe location, number of measurements, breath-holding, general rules of ROI cursor (Q-Box^™) positioning, and the definition of unreliable measurement for SSI were similar to those for ARFI [21]. For acquiring valid measurements, the operator located a 25 × 20 mm shear-wave imaging (SWI) box at vessel- and reverberation-free liver parenchyma and waited for at least three seconds for the elastogram to be stable, and finally put the 15 mm diameter Q-Box in the area of relatively uniform elasticity, which was seen as a uniform colored area in the SWI box. For each patient, ten consecutive LSMs were obtained within one Q-Box [22].