DESIGN OF A BINARY NEEDLE MANIPULATOR USING ELASTICALLY AVERAGED AIR MUSCLES FOR PROSTATE CANCER TREATMENTS

摘要

Affecting 1 out of 8 subjects in the U.S, prostate cancer is the most common form of cancer in men. Current medical procedures could be improved by the development of an MRI compatible (Magnetic Resonance Imaging) needle manipulator system, to precisely reach small tumors (<5 mm) inside the prostate. This paper presents and analyzes the potential of such a needle manipulator concept, based on hyper-redundant binary air muscles, all controlled by MRI compatible valves (e.g. piezoelectric or dielectric elastomer actuators). The proposed manipulator uses 12 polymer air muscles, each driven by 2 different actuation pressures, offering a total of 4096 (2~(12)) discrete needle positions. Based on a hyperelastic continuum mechanics air muscle model, a theoretical manipulator design is used to evaluate clinically-relevant design metrics, such as size, stiffness, workspace, accuracy and sensitivity. In this model, the manipulator's equilibrium configuration (for a given set of input pressures and applied forces) is found by minimizing the system's potential energy. The model capability is verified experimentally by a one degree of freedom (DOF) prototype. Simulation results show that the proposed elastically averaged air muscle concept can meet all design requirements. In particular, the needle workspace of about 70 mm by 80 mm entirely covers the prostate area, where targets are accurately reachable within 0.7 mm. Also, the pneumatic actuators can generate high forces leading to a system stiffness of ～4.6 N/mm at the needle tip. Such stiffness can adequately sustain the needle during insertion with minimal deflection to guaranty accurate positioning.