Visual servoing for intraoperative positioning and repositioning of mobile C-arms.

The problem of positioning mobile C-arms, e.g. for down the beam techniques, as well as repositioning during surgical procedures currently requires time, skill and additional radiation. This paper uses a Camera-Augmented Mobile C-arm (CAMC) to speed up the procedure, simplify its execution and reduce the necessary radiation. For positioning the C-arm in down-the-beam position, the pre-operative diagnostic CT is used for defining the axis. Additional CT visible markers on patient's skin allow the CAMC's optical camera to compute the C-arm's pose and its required displacement for positioning. In the absence of electronically controlled mobile C-arms, the system provides step-by-step guidance to surgical staff until the final position is achieved. At this point, the surgeon can acquire an X-ray to ensure the correct positioning. In the case of intra-operative repositioning, no pre-operative CT is required. X-ray/Optical markers allow the visual servoing algorithm to guide the surgical staff in C-arm repositioning using CAMC's optical camera. This work paves the path for many possible applications of visual servoing in C-arm positioning and in surgical navigation. Experiments on phantom and a cadaver study demonstrate the advantages of the new methods.