Although liver biopsy remains the reference standard for ﬁbrosis assessment, it has a number of inherent limitations, which have seen its clinical use decline over recent years. The invasive test is painful, results in hospitalisation in 3% of patients, and has a procedural mortality rate of approximately 0.01%.1.
The article explores in details:
- Low variability recommending 5 measurements instead of 10.
- High measurement reproducibility relative to the most widely used clinical elastographic tools.
- The low intrinsic measurement variability observed with this 2D SWE technique is likely attributable to the provision of the speed smart map and propagation map.
- Additional information may enable operators to better assess single shot acquisitions, allowing the rejection of acquisitions that are of insufficient quality for quantitative analysis1.
A new 2-dimensional (2D) shear wave elastographic (SWE) device has been developed for the noninvasive assessment of liver fibrosis. Guidelines on measurement acquisition parameters are not yet well established for this technique. Our study aimed to assess 2D SWE measurement variability and to determine the number of measurements required per patient to reliably assess liver stiffness.
Two-dimensional SWE was assessed in 55 patients with mixed-etiology chronic liver disease on an Aplio 500 ultrasound system (Toshiba Medical Systems Corporation, Tochigi, Japan). Ten measurements were obtained per patient by an operator blinded to all preceding readings. Results were analyzed with clinical information obtained from medical records.
The median interquartile range/median ratio for 2D SWE was 0.131 (quartiles 1–3, 0.089–0.174). Five readings provided an approximation within 0.11 m/s, or 4.2% of the median velocity of 10 measurements. Factors associated with increased measurement variability included body mass index (ρ = 0.388; P = .01), increased skin-to-liver capsule distance (ρ = 0.426; P = .002), and measurements taken within 1.5 cm of the liver capsule (P < .001). Measurements with heterogeneous shear wave profiles (indicated by a region of interest [ROI] SD/speed ratio > 0.15) showed greater deviation from the set’s median velocity than those with an ROI SD/speed ratio of 0.15 or lower (0.42 versus 0.22 m/s; P = .001).
Two-dimensional SWE showed low overall measurement variability, with a minimum of 5 readings providing equivalent precision to the existing method using 10 samples. Obesity, increasing abdominal wall thickness, subcapsular measurements and an ROI SD/speed ratio of greater than 0.15 were all associated with increased measurement variability. The ROI SD/speed ratio warrants further evaluation as a quality assessment metric, to allow objective operator assessment of individual 2D SWE measurement reliability in real time.
Speed smart map (1A) show the distribution of shear wave velocities through a section of liver, red areas representing high velocities and blue/green areas low velocities. Propagation map (1B) show the arrival time contours of shear waves. The ROI is positioned in an area with uniform shear wave characteristics, as indicated by homogeneous colour on the speed smart map and parallel contour lines on the propagation map.1
1. Nadebaum, D. P., Nicoll, A. J., Sood, S., Gorelik, A. and Gibson, R. N. (2018), Variability of Liver Shear Wave Measurements Using a New Ultrasound Elastographic Technique. J Ultrasound Med, 37: 647–656. doi:10.1002/jum.14375.