Photos of the experimental setup (A) and the four ex vivo studied samples (B,C,D,E). A 2-D matrix array probe was mounted on an axial linear motor. A compressor which fited the probe footprint was attached to it. The sample was positionned underneath in a cold water tank. Four different types of samples were studied: a gelatin gel with a soft layer at the top and a stiff layer at the bottom (B), a stiff gelatin inclusion embedded in a soft gelatin gel (C), a soft gelatin inclusion embedded in a stiff gelatin gel (D) and an ex vivo canine liver before and after an HIFU ablation (E).