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ftoiu
GheoneaUniversity of Medicine and Pharmacy Craiova, Romania
WEB—This is a Web exclusive article.
Sonoelastography is a recent imaging technique used for the real-time visualization of tissue elasticity [2]. The technique reveals the physical properties of the tissue by characterizing the difference in hardness between diseased tissue and normal tissue [2, 3]. The principle of elastography is that tissue compression produces strain (displacement) within the tissue and that the strain is smaller in harder tissue compared with softer tissue [2]. Consequently, the region of interest (ROI) for the elastography calculations is manually selected and should include the targeted lesion and the surrounding tissues [4, 5].
The technique of Friedrich-Rust et al. [1] is certainly interesting and deserves future studies with multicentric design and an increased number of patients. However, it is not clear exactly where Friedrich-Rust et al. placed the elastography ROI. According to the figure of tissue elasticity distribution from their article, the elastography ROI was placed inside the liver, consequently depicting differences in hardness among the various regions of the right liver lobe. Placement of the elastography ROI inside the liver would lead to important technical consequences and systematic errors in the measurements because the technique assumes computations relative to the average strain inside the ROI.
On the basis of our experience with liver elastography on 35 patients, we strongly suggest that the elastography ROI should also include the tissues surrounding the liver (Figs. 1, 2, 3). This would probably increase the accuracy of the technique, mainly because the surrounding tissues visualized through the intercostal space have a mixed strain that includes soft tissue (adipose tissue) and harder tissue (diaphragm and intercostal muscles). The structure of the anterolateral abdominal wall layers visualized through the intercostal space thus includes the skin, subcutaneous fatty tissue, intercostal muscles (external and internal), diaphragm, peritoneum, and liver tissue. In our experience, this technique has high accuracy for the differential diagnosis of liver steatosis, chronic hepatitis, and liver cirrhosis based on various degrees of liver fibrosis. In some patients, even the thin adipose tissue between the Glisson's capsule and visceral peritoneum (tela subserosa) can be depicted by the elastography software, although this is not visible on the conventional gray-scale image (Fig. 1).
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We have the same experience as the Friedrich-Rust et al. [1] concerning difficulty in performing sonoelastography in patients with increased body mass index (BMI). However, another window (for example, a subcostal window) could be used to better visualize the liver tissue. In our limited experience with the technique, liver steatosis has a distinct appearance on real-time sonoelastography images, with low mean hue histogram values (Fig. 1). Consequently, the presence of steatosis as a confounding factor in patients with chronic viral hepatitis should be further tested by multivariate analysis models because steatosis is an independent predictive factor that could modify the real-time elastography information.
We certainly agree with the Friedrich-Rust et al. [1] that future prospective studies with blinded comparisons and multicentric design should be designed to compare sonoelastography with other noninvasive techniques for the assessment of liver fibrosis (including transient elastography and MRI). Real-time sonoelastography should be also carefully assessed with studies that should also be designed to test the intra- and interobserver variability of the technique.
References
ftoiu A, Vilmann P, Ciurea T, et al. Dynamic analysis of
endoscopic ultrasound (EUS) elastography used for the differentiation of
benign and malignant lymph nodes. Gastrointest Endosc2007
(in press)
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This article has been cited by other articles:
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  R. Gulizia, G. Ferraioli, and C. Filice Open Questions in the Assessment of Liver Fibrosis Using Real-Time Elastography Am. J. Roentgenol., June 1, 2008; 190(6): W370 - W371. [Full Text] [PDF]
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A. Saftoiu, D. I. Gheonea, and T. Ciurea Reply Am. J. Roentgenol., June 1, 2008; 190(6): W372 - W373. [Full Text] [PDF]
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