Maelle Dejobert, Presenter: Nothing to Disclose

Patat Frederic MPH, MD, Abstract Co-Author: Nothing to Disclose

Jean-Pierre Remenieras, Abstract Co-Author: Nothing to Disclose

This project is a feasibility study of in vivo shear wave velocity measurements with a new processing algorithm.

Non-alcoholic fatty liver disease (NAFLD) is emerging as a major cause of liver disease. The accurate assessment of the type of NAFLD is crucial for prognostic evaluation. The only parameter classically measured by the existing US elastography method is the stiffness of liver tissue. Elastographic analysis of excised liver tissues have demonstrated that the complex shear modulus G* follows, as a function of frequency, a power law in biological tissue. The goal of this study was to estimate the speed of shear wave dispersion using a modified Fibroscan® in vivo.

Our work is a pilot study involving 10 healthy volunteers. We used a modified Fibroscan® research prototype based on transient elastography (Echosens company, France) to record shear wave dispersion at successive and different low frequency vibrations (25, 50, 75 and 100 Hz), and elastogram processing by using a new algorithm. For each volunteer, 40 transient vibrations were applied. We estimated the phase velocity dispersion cs(ω) of the shear wave as a function of the frequency in a 20-120 Hz bandwidth. The underlying premise for this work was to formulate the results with a fractional power law model cs(ω)= κcs*ω^γcs for which, the exponent coefficient γcs is a structure parameter of the liver, which is governed by viscosity and κcs is linked to elasticity. The comparison between experimental data and this fractional behaviour allowed us to determine these two biomechanical parameters of the liver, by solving an inverse problem. The measurement of cs(ω) was highly reproducible. For example, cs(50Hz) returned 1.44±0.20 m/s.

No simple biomechanical model (like the Voigt model) could be used to explain the frequency dispersion of cs(ω). Therefore, the challenge is still to determine the most suitable parameters κcs and γcs through fitting with our data. A prospective study is currently underway to determine whether analysis of the phase velocity dispersion can be used as a reliable tool for the diagnosis of NAFLD.

Dejobert, M, Frederic, P, Remenieras, J, Evaluation of Liver Viscoelasticity using Multi-frequency Transient Elastography: A New Approach Based on Fractional Power Law Behaviour.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004255.html