Providing accurate image-guidance for soft-tissue interventions remains a complex task. Most of the time, preoperative models and planning data are no more valid during the surgical process due to motions and deformations of the organ of interest. In this paper, two core components of a computer-assisted system for liver surgery are presented. One is an ultrasound segmentation techniques that allows for automatic liver vessels detection and the other is a mass-spring based deformable model used to update the shape of 3D models. Both have real-time capabilities and enable to update intraoperatively the data created during the planning phase.