The Research Of Viscoelastic Information Measurement Technique Based On Medical Ultrasound Elastography In The Evaluation Of Nonalcoholic Fatty Liver

Nonalcoholic fatty liver disease(NAFLD)is defined as the accumulation of lipid deposits in hepatocytes not due to excessive alcohol use.At present,the prevalence of this condition is approximately 20-30% of the general population in the coastal developed areas of China,and it threatens to become a serious public health problem.NAFLD represents a spectrum of diseases ranging from simple steatosis(SS)to nonalcoholic steatohepatitis(NASH),which can progress to liver fibrosis,cirrhosis,and hepatocellular carcinoma.Therefore,it is clinically important to distinguish SS from NASH and to assess the severity of hepatic fibrosis for riskstratified management of patients with NAFLD.In clinical practice,the non-invasive assessment of steatosis level is of great interest.Hepatic steatosis is linked to increased risk of death for cardiovascular and diabetic patients and it is associated with adverse peri-operative outcomes after partial hepatectomy.Liver biopsy remains the gold standard for diagnosing NAFLD,but it is invasive and associated with severe complications,and depends on surgical expertise and is subject to sampling error because of the small size of biopsy samples.Therefore,a simple and noninvasive method for confirming NAFLD is of major clinical interest.In recent years,ultrasound elastography has developed rapidly.This technique can measure mechanical properties of soft tissue with the noninvasive,fast,repeatable detection.The Acuson S2000 system has been widely used in clinical by the technology of acoustic radiation force impulse(ARFI)imaging for mapping mechanical responses of soft tissue.The basic principle of this method is that tissue in the region of interest is mechanically stimulated using short-duration acoustic pulses that are automatically produced by an ultrasound probe.The acoustic push pulse transmitted by the transducer toward the tissue induces elastic shear waves that propagate through the tissue.However,biological histological studies have shown that liver tissue is a viscoelastic material.ARFI technique is based on the elasticity model,which does not consider viscosity,and the significance of viscosity information for histopathology is unknown.According to the present research situation,the purpose of this paper is as follows:(1)To establish a set of viscoelasticity measurement system which can be applied to real-time measurement of soft tissue;(2)The accuracy of the experimental system should be verified;(3)To study the diagnostic ability of elasticity value and viscosity value in the evaluation of nonalcoholic fatty liver;(4)To study the ability of different viscoelastic models to characterize non-alcoholic fatty liver mechanical properties(5)To explore the difference of the linear elastic model and the line viscoelastic model in the evaluation of NAFLD.This paper carried a series of study in order to solve the above problems.Firstly,Verasonics system is designed to realize the Shear Wave Elastography(SWE)technique based on the line viscoelastic model,which enables the system to realize high-intensity acoustic radiation emission,high frame rate plane wave detection and viscoelasticity real-time display.At the same time,the accuracy of the measurement results is verified by viscoelastic phantom experiment.Secondly,the NAFLD rat model is established.Dynamics mechanical analysis(DMA)experiment is used to verify the effectiveness of SWE in the evaluation of rat model from the perspective of rheological mechanics.Thirdly,the shear wave velocity measured by DMA technique and SWE technique is used to evaluate the different Elasticity model.Finally,the results of ARFI experiment and SWE experimental results are compared to explore the difference between linear elasticity and linear viscoelastic model in the application of NAFLD.To summarize,a set of effective viscoelasticity measurement system based on SWE technology can be successfully applied in the study of NAFLD in rats.It is confirmed that the elasticity and viscosity value can be used to distinguish the SS group and NASH group and the different stages of fibrosis,indicating that the effect of viscosity is better to elasticity.Although the viscoelasticity values show significant power for estimating the severity of fibrosis in NAFLD,the presence of severe steatosis should always be considered to avoid overestimating liver fibrosis.Data analysis shows that voigt model is more suitable for describing the mechanical properties of rat NAFLD.The results show that the viscous parameters of the line viscoelastic model are optimal for the diagnosis of NAFLD.