Toward an MR-compatible needle holder with adaptive compliance using an active tensegrity mechanism

Introduction The field of MR imaging has extended from diagnosis to guidance and control in a wide variety of interventional procedures [1]. Due to the lack of space and manipulability within the MRI scanner, there is an ongoing interest for robotic assistance in MR-guided interventions. Numerous MR-compatible robots have been proposed, especially for needle manipulation. For needle insertion in the liver, patient-mounted robots are particularly interesting for the pro- vided partial compensation of the breathing motion. The needle holder must however still fulfill two contradictory requirements: it needs to be stiff during the insertion and compliant afterwards, in order to avoid organ lacerations [2]. This led to the development of needle grasping systems that allow the needle to move freely between two insertion phases [3]. In this paper, an alternate approach is considered: a needle manipulation system with adaptive compliance is proposed that is based on so-called tensegrity mechanisms. Numerous challenges related to MR-compatibility and compliance control could be overcome thanks to this recent class of robots, as outlined in the following through the design of a first device for needle orientation control.