To improve therapy research against cancer, we propose a robotized computer assisted system for needle insertion devoted to the small animal. The system is composed of a robotic arm on which the needle is attached and two cameras rigidly linked. It needs a preoperative CT acquisition in which the biologist defines an entry point and the target he wants to reach. The needle guidance is ensured by a visual servoing and the needle is registered in the CT frame using radio-opaque markers stuck beforehand on the small animal. Biologists estimate that such a system can be beneficial if the time preparation per animal remains below 15 minutes and if the insertion accuracy is within 1 mm. Several error sources can be identified: the error due to the system only, the organ repositioning error (due to breathing motions) and the error induced by the needle insertion. In this paper, we report an evaluation on living rats of the system error and of the organ repositioning error. Encouraging results show that a global accuracy of 0.9 mm may be reached with an acceptable preparation time.
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