Table 1.
Expected measurements and acoustic properties for the liver fibrosis phantoms represented with ±5% SD.
Fig 1.
The figure illustrates the method of 2D-SWE by GE performed on liver fibrosis phantom 3 with Young’s modulus 24.8 kPa ±5%. The color box (centre) represents the elastogram, and the circle represents the ROI where the elasticity measurement is acquired. The blue color indicates harder tissue, as semi-quantitatively presented by the color scale to the left.
Fig 2.
Samsung S-Shearwave Elastography assessed on liver fibrosis phantom 3. The yellow box (centre) represents the shear-wave measurement area. ROI and the RMI (Reliability Measurement Index) is expressed below the obtained elasticity measurement of 20.7 kPa.
Fig 3.
Hitachi SWM was applied on liver fibrosis phantom 3. The ROI is represented by the blue box (centre). The shear wave velocity measurements are presented in the histogram, and the median is given as Vs in m/s. Stiffness is based on this value expressed in kPa as well as the IQR (m/s), VsN (Reliability Index for shear wave velocity measurement) and the depth of the sample.
Fig 4.
Philips pSWE elastography is applied on liver fibrosis phantom 3. The shear wave measurement area is represented by the white box (center). The stiffness is shown in kPa on the left together with the unnumbered scale indicating the stiffness of the tissue, here shown towards hard.
Fig 5.
Fibroscan (Transient Elastography, TE).
This figure illustrates the assessment of transient elastography on liver phantom 3. 10 valid elastography measurements are listed on the right side, where also success rate and invalid measurements are reported. The IQR/median is used as a quality parameter, and aimed to be below 30% while obtaining a success rate of at least 60%.
Fig 6.
Variation in elasticity measurements for all systems for observer A.
The boxplot displays the median and the interquartile range, whiskers represent the 90th percentile of the measured elasticity by observer A for the four phantoms. The height of the box represents the measurement variability of the single observer for each of the phantoms. The horizontal axis represents the four phantoms with increasing stiffness; phantom 1 (2,7 ±0,14 kPa), phantom 2 (11,5 ± 0,57 kPa), phantom 3 (24,8±1,24 kPa) and phantom 4 (46,3 ± 2,32 kPa). The range each phantom stiffness is presented by the dotted lines within the figure. The vertical axis represents elasticity measurements (kPa) obtained by observer A. The colors represent the systems applied in the study: yellow, Philips iU22 (pSWE); blue, Samsung TS80A (pSWE); red, GE E9 (2D-SWE); green, Fibroscan (Transient Elastography) and purple, Hitachi Ascendus (SWM).
Fig 7.
Variation in elasticity measurements for all systems for observer B.
The boxplot displays the median and the interquartile range, whiskers represent the 90th percentile of the measured elasticity by observer B for the four phantoms. The height of the box represents the measurement variability of the single observer for each of the phantoms. The horizontal axis represents the four phantoms with increasing stiffness; phantom 1 (2,7 ±0,14 kPa), phantom 2 (11,5 ± 0,57 kPa), phantom 3 (24,8±1,24 kPa) and phantom 4 (46,3 ± 2,32 kPa). The range each phantom stiffness is presented by the dotted lines within the figure. The vertical axis represents elasticity measurements (kPa) obtained by observer B. For color representation, we refer to Fig 6.
Fig 8.
Mean elasticity measurements for both observers.
The figure shows the common mean for both observers within each phantom and for all systems. On the horizontal axis, the systems are listed with name, and on the vertical axis the mean elasticity measurements are expressed in kPa. The dotted line within the graph represents the elasticity of the respective phantom, provided by the producer. For color representation, we refer to Fig 6.
Table 2.
Mean and median of measurements for observer A (Mean/Median A) and B (Mean/Median B) in all liver fibrosis phantoms (1–4) and for all systems.
Fig 9.
IQR/Median (%) for all systems and both observers.
IQR/Median (%) is presented on the vertical axis for observer A (green) and B (yellow). The phantoms 1–4 are numbered on the horizontal axis.
Fig 10.
IQR/Median (%) for all systems and both observers.
IQR/Median (%) is presented on the vertical axis for both observers (blue). The phantoms 1–4 are numbered on the horizontal axis.
Table 3.
Level of significance for elasticity measurements between observer A and B, for all systems.
Fig 11.
Correlation between observers in measurement of each phantom for all systems.
The horizontal and vertical axes represent measurements by observer B and A, respectively. The unit measured is kilopascals (kPa). The line in the graph represents the line of unity. For color representation, we refer to Fig 6.
Fig 12.
The elastography system used are identified on the right side of the graph. The phantoms are identified by color, and represented in the upper right corner. The colors represent the four phantoms with increasing stiffness; yellow as phantom 1 (2,7 ± 0,14 kPa), green as phantom 2 (11,5 ± 0,57 kPa), red as phantom 3 (24,8 ± 1,24 kPa) and purple as phantom 4 (46,3 ± 2,32 kPa). The horizontal axis represents the common mean value of all measurements in both observers while the vertical axis represents the difference between individual measurements and this common mean (kPa), displaying the variability of measurements for the four phantoms. The black line within each system represents the common mean value, the dotted lines represent 95% Confidence Interval. A mean value close to 0 on the vertical axis means that the two observers apply the measurement scale without bias. If it deviates from 0, one of the observers tend to measure higher or lower values systematically compared to the other observer.
Table 4.
Inter- and intraclass correlation for both observers, for all systems.