We thank Ferraioli et al. for their interest in our article. We appreciate their concern, and would like to provide more details about how we measured liver stiffness using real-time tissue elastography.
With regard to the first question, we previously described how we set the region of interest (ROI) for measuring elasticity by real-time tissue elastography.[2, 3] The area of the ROI placed on both the liver and the spleen parenchyma was within 2 × 1 cm. The size of the ROI in the small vessels was usually within 0.3 × 0.5 cm. We used mean values derived from five measurements. We identified from these that the elastic ratio is not influenced by the size of the ROI. The maximum and minimum lengths of the ROI measured in our previous study were 1.90 ± 0.12 (range, 1.5-2.0) and 0.90 ± 0.11 (range, 0.6-1.0) cm for the liver and spleen parenchyma, and 0.44 ± 0.07 (range, 0.3-0.5) and 0.28 ± 0.01 (range, 0.2-0.3) cm for small vessels. We also previously found that interobserver agreement in determining fibrosis stage at different liver sites and the elastic ratio calculated by the two examiners closely correlated, and did not significantly differ. This evidence indicated that a small variation in the size of the ROI would not affect the value of the elastic ratio determined using real-time tissue elastography.
With respect to the second question, we carefully selected the ROI to exclude subcutaneous tissue. We confirmed the positioning of the ROI by comparison with a B-mode image when we set the ROI. This might be difficult to distinguish from the photograph in Supporting Fig. 2B, but the ROI was set within the liver parenchyma, and certainly excluded subcutaneous tissue.
We thank you again for your interest and questions, and we hope that real-time tissue elastography will become popular among clinicians and contribute to evaluating liver stiffness in patients with nonalcoholic fatty liver disease (NAFLD) and to the differential diagnosis of nonalcoholic steatohepatitis (NASH) for such patients.
Yoichi Hiasa M.D., Ph.D.
Hironori Ochi M.D., Ph.D.
Masashi Hirooka M.D., Ph.D.
Department of Gastroenterology and Metabology, Ehime University Graduate School of Medicine, Ehime, Japan