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We read with great interest the article by Ochi et al.[1] in the October 2012 issue of HEPATOLOGY and would like to express important concerns that arise from the analysis of Fig. 2 in the online version of the article. The figure shows how to obtain the liver elastic ratio, that is, the ratio of strain elastography distribution in two selected regions of interest (ROIs).

First, we want to point out that the ROI selected in the two images shown in Fig. 2A and Fig. 2B have different sizes, and both have a size that is much smaller compared with that of strain elastography's sample box. We believe that using an adjustable size of an ROI introduces a bias in calculating the elastic ratio. On the other hand, it is well known that in strain elastography the distribution of a color-coded strain in the sample box is complex. The criteria followed in choosing the size of the ROI and in positioning it in the sample box are not stated and they seem fairly subjective. There is a high risk of bias—which could hamper the results—when the examiner subjectively and arbitrarily chooses where to place the ROI for measurements in a complex color-coded strain area. In our opinion, a larger ROI, including all the area of the strain sample box, as has been done in other studies performed using strain elastography,[2] takes into account the complex distribution of the strain. Furthermore, it has been shown that strain elastography shows a patchy pattern of colors as liver fibrosis progresses from hepatitis to cirrhosis,[3] which could be overlooked by selecting a small ROI.

Second, the strain elastography sample box shown in Fig. 2B also includes the subcutaneous tissue. In strain elastography the stiffness is not an absolute value but is related to the surrounding tissue. The inclusion (as in Fig. 2B) or exclusion (as in Fig. 2A) of the subcutaneous tissue, which affects the color-coded strain image of the liver, also modify the elastic ratio.

  • Giovanna Ferraioli M.D.

  • Raffaella Lissandrin M.D.

  • Carlo Filice M.D.

  • Ultrasound Unit, Infectious Diseases Department, Fondazione IRCCS Policlinico San Matteo, Medical School University of Pavia, Pavia, Italy

References

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  2. References
  • 1
    Ochi H, Hirooka M, Koizumi Y, Miyake T, Tokumoto Y, Soga Y, et al. Real-time tissue elastography for evaluation of hepatic fibrosis and portal hypertension in nonalcoholic fatty liver diseases. Hepatology 2012;56:1271-1278.
  • 2
    Ferraioli G, Tinelli C, Malfitano A, Dal Bello B, Filice G, Filice C; Liver Fibrosis Study Group.Performance of real-time strain elastography, transient elastography, and aspartate-to-platelet ratio index in the assessment of fibrosis in chronic hepatitis C. AJR Am J Roentgenol 2012;199:19-25.
  • 3
    Tatsumi C, Kudo M, Ueshima K, Kitai S, Ishikawa E, Yada N, et al. Non-invasive evaluation of hepatic fibrosis for type C chronic hepatitis. Intervirology 2010;53:76-81.
  • 4
    Friedrich-Rust M, Ong MF, Herrmann E, Dries V, Samaras P, Zeuzem S, et al. Real-time elastography for noninvasive assessment of liver fibrosis in chronic viral hepatitis. AJR Am J Roentgenol 2007;188:758-764.
  • 5
    Morikawa H, Fukuda K, Kobayashi S, Fujii H, Iwai S, Enomoto M, et al. Realtime tissue elastography as a tool for the noninvasive assessment of liver stiffness in patients with chronic hepatitis C. J Gastroenterol 2011;46:350-358.