A Multi-view Opto-Xray Imaging System Development and First Application in Trauma Surgery Joerg Traub 1 , Tim Hauke Heibel 1 , Philipp Dressel 1 , Sandro Michael Heining 2 , Rainer Graumann 3 , and Nassir Navab 1 1 Computer Aided Medical Procedures (CAMP), TUM, Munich, Germany 2 Trauma Surgery Department, Klinikum Innenstadt, LMU Munich, Germany 3 Siemens SP, Siemens Medical, Erlangen, Germany Abstract. The success of minimally invasive trauma and orthopedic surgery procedures has resulted in an increase of the use of fluoroscopic imaging. A system aiming to reduce the amount of radiation has been introduced by Navab et al. [1]. It uses an optical imaging system rigidly attached to the gantry such that the optical and X-ray imaging geometry is identical. As an extension to their solution, we developed a multi-view system which offers 3D navigation during trauma surgery and ortho- pedic procedures. We use an additional video camera in an orthogonal arrangement to the first video camera and a minimum of two X-ray im- ages. Furthermore, tools such as a surgical drill are extended by optical markers and tracked with the same optical cameras. Exploiting that the cross ratio is invariant in projective geometry, we can estimate the tip of the instrument in the X-ray image without external tracking systems. This paper thus introduces the first multi-view Opto- Xray system for computer aided surgery. First tests have proven the accuracy of the cali- bration and the instrument tracking. Phantom and cadaver experiments were conducted for pedicle screw placement in spinal surgery. Using a postoperative CT, we evaluate the quality of the placement of the pedicle screws in 3D. 1 Introduction Mobile C-arm systems are established in everyday routines in orthopedic and trauma surgery. The trend toward minimally invasive applications increases the use of fluoroscopic images within surgery and thus the radiation dose [2,3]. Nowa- days the combined use of mobile C-arms, that are capable of 3D reconstruction, and a tracking system provide navigation information during surgery, e.g. [4]. Systems using this technique use so called registration free navigation methods based on a mobile C-arm with 3D reconstruction capabilities tracked by an ex- ternal optical tracking system. The imaging device is tracked and the volume is reconstructed in the same reference frame in which the instruments and the pa- tient are tracked. Hayashibe et al. [5] combined the registration free navigation approach using an intra-operative tracked C-arm with reconstruction capabilities and in-situ visualization by volume rendered views from any arbitrary position of a swivel arm mounted monitor. N. Ayache, S. Ourselin, A. Maeder (Eds.): MICCAI 2007, Part II, LNCS 4792, pp. 18–25, 2007. c  Springer-Verlag Berlin Heidelberg 2007