Design of a robotic tool for percutaneous instrument distal tip repositioning.

Manually performed image-guided percutaneous procedures are limited by targeting errors due to instrument misalignment, deflection and an inability to reposition the distal tip of the instrument after it has been percutaneously inserted. These limitations result in suboptimal instrument positioning that limits diagnosis and treatment for a variety of procedures as well as excessive procedure time and radiation dose (in the case of x-ray based imaging). Hence we are developing a robotic tool capable of repositioning the distal tip of a percutaneous instrument after a single insertion into the body. It is based on the concept of deploying a super-elastic pre-curved stylet from a concentric straight cannula. The proximal end of the cannula is attached to the distal end of a screw-spline that enables it to be translated and rotated with respect to the casing. Translation of the stylet relative to the cannula is achieved with a second threaded screw with a splined groove. The device is made of mostly plastic components and actuation is achieved using micro-stepper motors. Measurements of the maximum axial force for the cannula screw-spline and stylet screw were found to match those from design calculations. Evaluation of the mechanism positioning capability demonstrated sub-millimeter and sub-degree translation and angular accuracy. We foresee this robotic tool having wide application across a range of procedures such as biopsy, thermal ablation and brachytherapy seed placement.