Design and Optimization of a Novel MRI Compatible Wire-Driven Robot for Prostate Cryoablation

Giving assistance to radiologists during percutaneous procedures under MRI is currently a great challenge for roboticists: the limited space inside the scanner and the presence of an intense magnetic field introduce strong design constraints. In this paper, we present a novel robotic assistance for prostate cryotherapy under MRI guidance. An MR-compatible wire-driven mechanism with embedded sensors is proposed to optimize the device compactness. To this end, a design methodology of wire-driven manipulators is first introduced and applied in our context. This design methodology is achieved in two steps, using an algorithm that optimizes the available wrench set and a numerical approach based on interval analysis for results validation. In order to develop a fine control of the device, an original instrumented structure is proposed that allows the evaluation of the tensions in the cables. The synthesis approach of the instrumented structure is presented before introducing the prototype of the device.