Ultrasound (US) imaging could potentially play a major role in the field of Computer Assisted Surgery (CAS). For doctors and surgeons to make full use of CAS tools in planning and executing surgical operations, they also need user-friendly automatic software based on fast, precise and reliable registration algorithms. The main goal of this paper is to take advantage of the segmentation/registration duality to extract the relevant information from US images. This information will allow the precise and automatic registration of anatomical structures contained in the pre-operative model and of intra-operative data contained in US images. The result of registration will be further used to guide a computer-assisted intervention such as orthopedics or radiotherapy.