| Fibroscan® (Echosens, Paris, France) is a parametric transient elastography based device used to quantify liver fibrosis by following the propagation of a low frequency shear wave and measuring the mean Young’s modulus of the liver. This device has been successfully applied to homogeneous tissues such as liver in patients with chronic hepatic diseases. Current developments in transient elastography target the characterization of heterogeneous tissues. The objective of this study is to investigate the potential of parametric transient elastography in the characterization of heterogeneous tissues such as liver with heterogeneous fibrosis or tumors. The estimation of the shear wave velocity can be achieved by solving the elastic wave equation taking into account either the 1D, the 2D or the 3D components of the displacement spatial derivatives. Two methods are investigated: A 1D direct local inversion is performed on data acquired with a standard Fibroscan® probe composed of a 3.5 MHz transducer mounted on a low frequency vibrator and a 3D direct local inversion is achieved on data acquired using a new dedicated multi-elements probe connected to an ultra-fast ultrasonic device. The algorithms are validated on simulations and on heterogeneous phantoms and tested on data acquired in the liver in vivo. |