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.

USPSTF Finalizes AAA Screening Recommendations

By Erik L. Ridley, AuntMinnie staff writer

June 24, 2014 -- Adhering mostly to its draft statement published in January, the U.S. Preventive Services Task Force (USPSTF) included no big surprises in its new recommendations in favor of ultrasound screening for abdominal aortic aneurysms (AAAs).

In a notable change from its previous 2005 statement, the task force added nuance to its recommendations for ultrasound screening for AAA in women, providing separate guidance for women who have smoked and those who haven't. In 2005, USPSTF recommended against screening in all women; however, the task force has now concluded that current evidence is insufficient to assess the balance of benefits and harms of ultrasound screening in women 65 to 75 who have ever smoked. It continues to recommend against screening in women who have never smoked.

The final recommendations, which were published online June 23 in the Annals of Internal Medicine, also retained the task force's 2005 B-grade recommendation for one-time ultrasound screening for AAA in men 65 to 75 who have ever smoked. In keeping with a change to the definition of its C grade level, USPSTF now suggests selective screening for men of this age group who have never smoked. In 2005, the same C grade level indicated that the task force made no recommendation for or against screening.

AAA screening in women

The task force noted that only one randomized, controlled trial on AAA screening included women, and the trial found no difference in AAA rupture, AAA-specific mortality, or all-cause mortality between screened women and a control group. The group also pointed out that women age 70 years who have ever smoked have an overall AAA rupture prevalence of approximately 0.8%, while current smokers have a prevalence of approximately 2%.

"However, the single [randomized, controlled trial] of screening for AAA that included women was underpowered to draw definitive conclusions by sex, and the prevalence of AAA in women who currently smoke approaches that of men who have never smoked," they wrote. "As such, a small net benefit might exist for this population and appropriate, high-quality research designs should be used to address this question."

As a result, the task force determined that the evidence was inadequate to conclude whether one-time ultrasound screening for AAA was beneficial in women ages 65 to 75 years who have ever smoked.

The task force also said that the prevalence of AAA in women who have never smoked ranges from only 0.03% to 0.6% for ages 50 to 79, and there is no evidence of apparent benefit of screening for AAA in this group of women.

"The USPSTF therefore concludes that adequate evidence shows that the absolute benefit of one-time screening for AAA with ultrasonography in women who have never smoked can effectively be bounded at none or almost none," the group wrote.

The task force also observed that women had a slightly higher risk of AAA surgery-related death than men. Women had 7% operative mortality with open repair, compared with 5% for men, and 2% for endovascular repair, compared with 1% for men.

"Convincing evidence shows that the harms associated with one-time screening for AAA with ultrasonography are at least small in all populations and potentially higher in women because of their higher risk for operative mortality," they wrote.

AAA screening in men

The task force reiterated that there is convincing evidence that one-time ultrasound screening for AAA yields a moderate benefit in men ages 65 to 75 years who have ever smoked. However, the lower prevalence of AAA in men who have never smoked substantially reduces the absolute benefit of screening in this group of men.

"Despite the demonstrated benefits of screening for AAA in men overall, the lower prevalence of AAA in male never-smokers versus male ever-smokers suggests that clinicians should consider a patient's risk factors and the potential for harm before screening for AAA rather than routinely offering screening to all male never-smokers," the task force wrote.

The group noted that important risk factors for AAA include older age and a first-degree relative with an AAA; other risk factors include a history of other vascular aneurysms, coronary artery disease, cerebrovascular disease, atherosclerosis, hypercholesterolemia, obesity, and hypertension. Also, factors associated with a reduced risk for AAA include African-American race, Hispanic ethnicity, and diabetes.

Draft changes

Changes made to the draft version included clarification of the definition of an "ever-smoker" and information about the absolute benefits of screening for AAA to provide additional context for the reported reductions in relative risk, according to the task force. USPSTF also expanded the discussion relating to the risks and benefits of screening and treatment in women compared with those in men.

"Finally, the USPSTF emphasized that more research -- including high-quality modeling studies -- is required to better understand the relative benefits and harms of screening for AAA in men and women with a family history of AAA and for women who have ever smoked," they wrote.

Related Reading

EHR alerts boost participation in AAA screening, February 12, 2014

USPSTF revises stance on ultrasound AAA screening, January 28, 2014

Longer US surveillance intervals fine for men with small AAAs, February 26, 2013

VC goes extra innings with AAA screening, November 12, 2012

AAA ultrasound screening hasn't saved many lives in Medicare, October 2, 2012

Copyright © 2014 AuntMinnie.com