Design, calibration and evaluation of a robotic needle-positioning system for small animal imaging applications.

A needle-positioning robot has been developed for image-guided interventions in small animal research models. The device is designed to position a needle with an error < or =100 microm. The robot has two rotational axes (pitch and roll) to control needle orientation, and one linear axis to perform needle insertion. The three axes intersect at a single point to create a remote centre of motion (RCM) that acts as a fulcrum for the orientation of the needle. The RCM corresponds to the skin-entry point of the needle into the animal. The robot was calibrated to ensure that the three axes intersected at a single point defining an RCM and that the needle tip was positioned at the RCM. Needle-positioning accuracy and precision were quantified in Cartesian coordinates at ten target locations in the plane of each rotational axis. The measured needle-positioning accuracy in free space was 54 +/- 12 microm for the pitch axis plane and 91 +/- 21 microm for the roll axis plane. The measured needle-positioning precision was 15 and 17 microm for the pitch and roll axes planes, respectively. The robot's ability to insert a needle into a tumour in a euthanized mouse was demonstrated.