Shear viscosity measurement using Vibration- Controlled Transient Elastography

Vibration-Controlled Transient Elastography (VCTE^¿) has been successfully applied to quantify stiffness in the liver of human patients with chronic viral hepatitis C. However, this technique is based on the measurement of the shear wave group velocity and does not take advantage of the shear wave dispersion in the frequency domain, which is related to the viscosity of the medium. In this work, we propose two methods to measure shear viscosity using VCTE^¿. The first method is based on the measurement of the shear wave phase velocity at several frequencies. The second method relies on the decrease of the signal spectral centroid as a function of depth. These methods are first tested on simulated data obtained using a Green´s function approach. Simulations are performed for shear wave velocities in the range of 1.0 to 4.5 m/s and shear viscosities in the range of 0.5 to 3.0 Pa.s. They show that using these techniques, it is possible to measure shear viscosity using VCTE^¿. Shear viscosity measurements are also performed in the liver in vivo. The mean shear viscosity obtained from 6 healthy volunteers is close to 1.8 Pa.s.