How many measurements are needed for liver stiffness assessment by 2D-Shear Wave Elastography (2D-SWE) and which value should be used: the mean or median?

To analyze how many measurements are needed for non-invasive assessment of liver stiffness (LS) by means of 2D-Shear Wave Elastography (2D-SWE) and if the use of mean of median values of 2D-SWE measurements is needed. Methods: We evaluated 449 consecutive subjects (with or without chronic liver disease) by means of Transient Elastography (TE) and 2D-SWE. We compared the correlation of LS assessed by TE with 2D-SWE measurements when using either the median of 5 valid 2D-SWE measurements or the mean of 3 or 5 valid 2D-SWE measurements. Results: We obtained reliable LS measurements by TE in 330/449 subjects (73.5%). From these, in 281 subjects we obtained 5 valid 2D-SWE measurements. The correlation of LS assessed by TE with 2D-SWE values was similar when we used the median value of 5 valid 2D-SWE measurements, the mean value of 5 valid 2D-SWE measurements or the mean value of 3 valid 2D-SWE measurements: r=0.683, r=0.711 and r=0.691, respectively. There were no significant differences between the median value of 5 valid 2D-SWE measurements; the mean value of 5 valid 2D-SWE measurements; or the mean value of 3 valid 2D-SWE measurements: 7.6 kPa, 7.7 kPa and 7.6 kPa, respectively. Conclusions: Our study showed that it is enough to perform 3 valid 2D-SWE measurements and to use the mean value of these measurements.