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Thứ Ba, 1 tháng 7, 2014

US Elastography for Diffuse Liver Disease: Weaknesses and Strengths


US Elastography: Weaknesses and Strengths


The most significant challenge facing US elastography is the issue of measurement reproducibility. A number of studies concerning this issue have been published; however, many investigators have brought up questions about this issue due to the inherent limitations of US such as the operator-dependent performance. 
Transient elastography is a highly reproducible and user-friendly technique [45], and liver stiffnessmeasurementby transient 
elastography does not require a learning curve: even a novice can obtain a reliable result after a single training session [46]. However, because liver stiffness measurements can be influenced significantly by steatosis, obesity, lower degrees of hepatic fibrosis [45], necroinflammation of hepatocytes [47], cholestasis [48], elevated central venous pressure [49], and even postprandial conditions [50], it should be carefully applied when used as an alternative measurement of liver
stiffness instead of liver biopsy.

In the case of ARFI, the overall reproducibility is also not bad, having an intraclass correlation coefficient (ICC) value for the interrater observation of 0.81 and an ICC for the intrarater observation of 0.90. However, gender (women), high body mass index, ascites, and lower degree of liver disease (noncirrhotic patients) are considered factors that impede the reproducibility of ARFI [51].
In the case of SSI, the inter- and intraobserver agreements have ICC values of 0.88 and 0.94, respectively, which are similar to the results of ARFI imaging [52].




Despite the issues described above, US elastography has  many advantages in clinical fields. The most important aspect is convenience, as is the case with most ultrasonography examination techniques. Indeed, US elastography is fast, easy to use, and portable, so much so that it can be performed at the patient’s bedside. Likewise, because it does not use ionizing radiation, US elastography is relatively safe, even in patients who repeatedly undergo the procedure. US elastography is also less expensive than MR elastography [53]. Going forward, the most important strength of US elastography is the availability of a large amount of accumulated clinical data that have demonstrated its clinical usefulness, although most of these data are related to transient  elastography.




Conclusions

Measurement of liver stiffness using various technical developments is evolving to overcome its limitations. Recently, the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) published an informative guideline for the use of US elastography [54,55] that deals with the relevant technology and clinical applications. Along with the basic principles for use, these guidelines include the practical advantages and disadvantages of US elastography as well as recommendations for the examination of various body parts. According to these guidelines, US elastography is useful to assess the severity of liver fibrosis in patients with diffuse liver disease and particularly to distinguish patients with nil to mild fibrosis from those with significant fibrosis, although some of the newer techniques must be validated through clinical studies. At present, however, US elastography for the differentiation of focal hepatic lesions is not recommended.


In conclusion, US elastography is useful for diagnosing hepatic fibrosis in patients with CLD and may be used as a convenient and non-invasive surveillance method to estimate the prognosis of patients with fatal complications related to CLD. Accordingly, the development of a standardized method for liver stiffness measurement and technical improvements should be a priority for the clinical application of US elastography. Together, these efforts will significantly enhance the clinical implications of US elastography.
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