Discretely Actuated Steerable Cannula
Elif Ayvali1, Chia-Pin Liang1,2, Mingyen Ho1, Yu Chen1,2, Jaydev P. Desai1
1 Robotics, Automation, and Medical Systems (RAMS) Laboratory; Maryland Robotics Center, Institute for Systems Research; Department of Mechanical Engineering, University of Maryland, College Park, USA
2 The Fischell Department of Bioengineering, University of Maryland, College Park, USA
Abstract
In percutaneous needle-based procedures such as prostate biopsy, breast biopsy and radio frequency-ablation (RFA), a needle is used to reach a target location or a region. The needle is maneuvered at the distal end and due to needle and soft-tissue interaction it may be re-introduced or withdrawn slightly to correct for the error in targeting. Nonlinear and non-homogeneous nature of the soft-tissue and the presence of anatomical obstacles make trajectory planning and execution challenging. The goal of our research is to develop a discretely actuated needle/cannula that can generate localized forces to correct for errors in trajectory execution.
The discretely actuated steerable cannula is made of straight segments that are connected by shape memory alloy (SMA) actuators. SMA actuators are annealed in arc shape and antagonistic SMA actuators are placed at discrete locations along the cannula length to enable local bending and a small radius of curvature in trajectory planning. The hollow inner core design of the cannula enables the introduction of both diagnostic and therapeutic tools and hence the cannula can be potentially used for both percutaneous and intra-vascular procedures. We fully characterized the SMA actuator and correlated the strain in the SMA actuator with the temperature and the external stress acting on the SMA actuator. This enables us to control the bending angle at each joint by controlling the temperature of the SMA actuator. We have developed two pulse width modulations (PWM)–based control schemes, namely PWM based temperature feedback and PWM based vision feedback control. PWM is mainly used to drive the SMA actuators and enables multiple joint motion. We have also developed motion planning algorithms to guide the cannula to a desired location and we demonstrated the capability of the cannula to aid in diagnosis by guiding an optical coherence tomography (OCT) probe to perform microscale imaging.
Related Publications
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Ayvali E, Ho M and Desai JP. A novel discretely actuated steerable probe for percutaneous procedures. In: 12th International Symposium On Experimental Robotics, New Delhi, India, 18–21 December 2010.
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Ayvali E and Desai JP. Towards a discretely actuated steerable cannula. In: 2012 IEEE International Conference On Robotics and Automation (Accepted for publication)., Minnesota, USA, 14–18 May 2012.
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Ayvali E, Liang CP, Ho M, Chen Y and Desai JP. Towards a discretely actuated steerable cannula for diagnostic and therapeutic procedures, The International Journal of Robotics Research (Accepted for publication).
Links
http://rams.umd.edu/html/cannula.shtml
http://rams.umd.edu/html/resource.shtml#video