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Abstract

We were pleased to read this comment addressing our recent article comparing supersonic shear imaging (SSI) and transient elastography (TE) by using the XL probe in the staging of liver fibrosis in overweight and obese patients.1Yoneda M. et al.Clin Gastroenterol Hepatol. 2015; 13: 1502-1509Google Scholar We agree that data from several distinct centers would help to evaluate the utility of elastographic methods in the evalution of obese populations. First, for the precise description of failure and unreliability of SSI, we used 5 valid readings that used a Q-box size of 10 mm, an interquartile range >30% was considered to be unreliable, and a success rate <60% was considered to be failure as described in Sporea et al.2Sporea I. et al.Ultrasound Med Biol. 2013; 39: 1933-1941Google Scholar This definition was already included, and the corresponding reference was listed in our supplementary materials. Second, Thwaites et al mentioned that failure rates were significantly associated with evaluation by different operators. However, SSI has been reported to demonstrate consistent intraoperator reproducibility with an intraclass correlation coefficient of 0.95 and an acceptable interoperator reproducibility (intraclass correlation coefficient = 0.88).3Ferraioli G. et al.Eur J Radiol. 2012; 81: 3102-3106Google Scholar Therefore, the intraoperator and interoperator reproducibility of SSI warrants further study. Finally, concerning the discordance between SSI and TE, it is known that these methodologies do not lead to strictly identical liver stiffness measurements (LSMs); however, the LSMs obtained by using either methodology demonstrate strong correlation. The differences between SSI and TE have been studied extensively and have been shown to result from the fact that the shear wave is derived from the broadband (60–600 Hz) characteristic of the mechanical excitation generated by using acoustic radiation force for SSI, whereas TE elasticity values are generated by using an external vibrator (50 Hz).4Bavu E. et al.Ultrasound Med Biol. 2011; 37: 1361-1373Google Scholar In fact, SSI values derived from a shear wave of 50 Hz (assessed by shear wave spectroscopy) were reported to provide values that strongly correlated with TE.4Bavu E. et al.Ultrasound Med Biol. 2011; 37: 1361-1373Google Scholar As expected, increased skin-to-capsule distance may affect the discordance of LSMs obtained by using either methodology as demonstrated by Thwaites et al. Supersonic Shear Imaging and Transient Elastography in ObesityClinical Gastroenterology and HepatologyVol. 14Issue 3PreviewWe read with interest the article by Yoneda et al1 that compared supersonic shear imaging (SSI) and transient elastography (TE) using extra-large (XL) probe in the staging of liver fibrosis in a prospective study of 258 overweight and obese patients with chronic liver disease.1 The investigators concluded that SSI and the TE-XL probe each accurately assessed the degree of liver fibrosis as compared with histologic analysis and that there was a strong correlation with TE and SSI results. These are important findings because the utility and accuracy of noninvasive methods to assess liver fibrosis in the obese population remains a concern. Full-Text PDF