Editors: Ioan Sporea, Roxana Șirli

Hepatic Elastography Using Ultrasound Waves

Special Offer (PDF + Printed Copy): US $84
Printed Copy: US $84
ISBN: 978-1-60805-557-9 (Print)
ISBN: 978-1-60805-463-3 (Online)
Year of Publication: 2012
DOI: 10.2174/97816080546331120101

Introduction

Some time ago, Schiano raised the question "To B or not to B", which means "To Biopsy or not to Biopsy" the liver for the evaluation of chronic hepatopathies. For a long period, liver biopsy (LB) was considered the "gold standard" for the evaluation of liver morphology. A major disadvantage of LB is its invasiveness: the risk of post-biopsy discomfort for patients and sometimes, for serious complications; also the lack of sensitivity to detect fibrosis, due to its heterogeneity; and the inability to obtain good quality fragments, adequate for pathological examination. In these conditions, the question is whether LB can be regarded as the "gold standard" for staging and grading chronic hepatitis in daily activity.

But what alternative can we propose for the evaluation of liver fibrosis at this moment? The answer is: non-invasive methods and the ultrasound elastographic ones presented in this volume.

Transient Elastography (FibroScan, Echosens) is a recognized method in many countries. Published papers and meta-analyses showed the value of this method for the diagnosis of liver cirrhosis (AUROC - 94%); for staging chronic HCV hepatitis (a cut-off value of 7.5 kPa differentiates F0–1 from F2–4 with 67% sensitivity, 87% specificity, 86% positive predictive value (PPV) and 68% negative predictive value (NPV), with a diagnostic accuracy of 76%; but also in HBV chronic infection, NASH, PBC, PBS).

Acoustic Radiation Force Impulse (ARFI) Elastography (Siemens S2000) is another elastographic methods with promising results (a meta-analysis showed that the mean diagnostic accuracy of ARFI expressed as AUROC was 0.88 for the diagnosis of significant fibrosis (F≥2), 0.91 for the diagnosis of severe fibrosis (F≥3), and 0.93 for the diagnosis of liver cirrhosis. In the subgroup of patients who underwent both ARFI and TE, the diagnostic accuracy of ARFI was comparable to TE for the diagnosis of significant and severe fibrosis, with a trend to be inferior for the diagnosis of cirrhosis. The future of liver fibrosis evaluation points towards non-invasive methods, decreasing dramatically the number of liver biopsies.

Studies have been published regarding the value of Real Time Elastography, performed for the first time with Hitachi systems (EUB-8500 and EUB-900), which uses an extended combined autocorrelation method to produce a real-time elasticity image by using a freehand approach to compress the tissues with the ultrasound transducer. The relative tissues’ elasticity is calculated and displayed as a color overlay on the conventional B-mode image. HiRT-E could be a promising method for the evaluation of liver fibrosis in chronic hepatopathies, but new methods of color code interpretation are needed to improve the accuracy, as well as a reference acquisition methodology.

ShearWave™ Elastography, the new "kid on the block", produces an image where true local tissue elasticity is displayed in a color map in "real time". Elasticity is displayed using a color coded image superimposed on a B-mode image. Stiffer tissues are coded in red and softer tissues in blue, with an image resolution of approximately 1mm. The true elasticity is assessed based on Shear wave propagation speed into the tissue. It is a very new method and only small studies were presented at international meetings.

Thus, having the alternative of noninvasive elastographic methods for the evaluation of liver fibrosis (maybe together with serum tests such as FibroMax) and knowing the low real life yield of liver biopsy (and the risk of complications), we can safely conclude that, for daily medical activity, liver biopsy can be avoided in the vast majority of cases.

This ebook presents an interesting set of chapters on the subject and is of good value to hepatologists interested in non invasive diagnostic methods for liver diseases.

Preface

Liver chronic diseases become more and more frequent in daily medical practice, despite of medical progress in the treatment of chronic viral hepatitis. The incidence of diseases such as non-alcoholic steato-hepatitis (NASH) or alcoholic steato-hepatitis (ASH) increases in many regions of the world (especially in Europe and the USA), but the evaluation of chronic hepatitis HCV or HBV still represents a major challenge for the hepatologist, internal medicine or general practitioner. The evaluation of cholestatic diseases, of autoimmune hepatitis or of post-transplant patients is another field in which hepatologists try to find solutions.

Traditionally, liver biopsy is used for chronic liver diseases staging and grading, but this method is not very well accepted by patients and usually it is rarely repeated during the follow-up. In the last years, non-invasive modalities for the evaluation of chronic hepatopathies became more and more popular, especially in Europe. Blood tests and elastographic methods for liver stiffness assessment become part of routine evaluation of patients with chronic liver diseases. Ultrasound based elastographic methods for the evaluation of liver stiffness started with Transient Elastography, but in the last 2-3 years, other methods that use ultrasound waves opened the door of hepatology. Acoustic Radiation Force Impulse Elastography, Real Time Elastography or Shear Wave Elastography are now available, trying to prove their value for liver stiffness assessment as a marker for fibrosis or for the evaluation of liver masses in the liver.

Thus, so much new information concerning the non-invasive evaluation of liver fibrosis or of liver masses, in such a short time, can make the practician to have some problems concerning these methods, such as the types of waves used, or the results of the examinatiotn, that can be expressed in kiloPascals or in meters/second, with a large values spectrum.

In this eBook we try to clarify some notions regarding elastography, which we think that will be useful for practitioners (fellows in training or specialists): what is transient elastography or shear waves elastography, from physics point of view; how do different types of elastography work and which are the differences between them; and, finally, which is their practical value (scientific proves) methods. Surely, this field is a very dynamic one, and each month papers are published showing new results of these methods.

Thus, the aim of this eBook is to show how ultrasound wave based elastographic methods work and which their results in the field of hepatology are. We hope that the level of presentation (especially information regarding the physics of elastography) is adapted to the medical personnel, making this eBook useful for daily practice of everyone interested in this field.

Ioan Sporea
Roxana Șirli

Department of Gastroenterology and Hepatology
“Victor Babeș” University of Medicine and Pharmacy Timișoara
Romania

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