Shear wave elastography of a liver fibrosis mouse model using a high frequency ultrasound system with mechanical scanning

Abstract

Liver fibrosis is one of the most common chronic liver diseases and has long serious consequence for patient's morbidity and mortality. As the liver fibrosis often involves the changes of mechanical properties, shear wave elastography (SWE) can be a promising tool for diagnosis of hepatic fibrosis. In clinical applications, SWE is generally performed with an array system at relative low frequencies (<20MHz). For preclinical studies on small animals, on the other hand, a high frequency (> 30MHz) single element transducer with mechanical scanning may still be used. In addition, high frequency transducers (both array and single element transducers) may not be able to produce shear wave with sufficient amplitudes for detection and estimation. Consequently, the objective of this study is to develop a high frequency platform for evaluation of liver fibrosis on mice using SWE. The platform uses a 40MHz single element transducer for imaging and a separate 20MHz transducer for producing radiation force and shear waves. Liver fibrosis is induced in 10 mice using carbon tetrachloride (CCl 4 ); 10 mice served as control group. Special pulse sequence was also designed so that shear wave propagation can be monitored and measured with this mechanical scanning setup. Liver elastic properties were measured in vivo by analyzing shear wave dispersion combined with a Voigt model fitting. The animals were then sacrificed and the stages of fibrosis were analyzed using METAVIR score. The measured mean values of shear elasticity ranged from 1.06 to 1.89 kPa for normal (stage F0) and fibrosis stages with METAVIR score of F 3 -F 4 , respectively. The spearman correlation coefficient presents a high correlation between the measured elasticity and fibrosis stages (0.73, p<0.001). Based on these results, elasticity measurements using this high frequency SWE platform can provide quantitative assessment of liver fibrosis stages. In other words, this new imaging platform that combines the advantages of high frequency ultrasound and SWE can be a promising tool for studying the progression of liver fibrosis on pre-clinical animal models non-invasively and quantitatively.