MRGuide - Robotic Assistance for Percutaneous Procedures on the Prostate
MRI is of particular interest for percutaneous procedures. MR scanner indeed provides a high level of details for soft tissues, and the scanner does not use any harmful ionizing radiations. For prostate cancer, one of the most widespread type of cancer, MR-guided tissue biopsy and tumor destruction using cryotherapy constitute therefore very promising techniques.
Today, needle guidance remains however a very delicate task. The radiologist must be highly trained to determine from 2D images the correct position and orientation of the needles with respect to the patient. In this project, we therefore propose to introduce a robotic assistance to simplify the procedure and help developing MR-guided techniques on the prostate.
Two major aspects are being developed: the first one is the design of the robotic device, based on a cable-driven robot. It implies in particular the development of an instrumented structure to get the evaluation of the cable tensions while being in the MR room. The second major aspect is the control of the robot: a significant distance exists between the actuators and the end-effector and high friction can occur in the selected cable transmissions. A custom control architecture needs to be designed to ensure that the stiffness of the robot end-effector is maintained and the level of cable tensions is correct.
Keywords: MR compatible robotics, prostate cryotherapy, compliant mechanisms, design and control of cable-driven mechanisms
Pierre Renaud, Bernard Bayle, Laurent Barbé
The project is developed in collaboration with the Radiology Department of the Civil Hospital of Strasbourg (Prof. A. Gangi).
Cable-driven robot for needle guidance
The MRGuide robotic assistant is designed by considering that the radiologist only needs an assistance in the 3D positioning of the needle. The needle insertion is performed by the radiologist, to get a haptic feedback during the insertion.
MR compatiblity is very difficult to obtain: the scanner is very sensitive to any active device introduced in the MR room, and conversely any robotic system can be influenced by the scanner. The existence of a strong magnetic field is in particular a severe design constraint. In order to get an excellent MR compatibility, and provide a very compact and lightweight device, a cable-driven robot is proposed, with remote actuation using Bowden cables to connect the device to the motors located outside the MR room. Compactness, MR compatibility, ease of use are combined.
- The prototype of the device is fully MR-compatible, weights only 120g and is very compact
- An original control of the wire-driven robot has been implemented that takes advantage of the local mesurement of the cable tensions, inside the MR scanner