Waterjet Steerable Needles: A New Promise for Improving Medical Procedures
Primary author: Mahdieh Babaiasl
Co-author(s): Fan Yang; John Swensen
Faculty sponsor: John P. Swensen
Primary college/unit: Voiland College of Engineering and Architecture
Steerable needles are a type of medical devices that can steer around obstacles to reach to a target location within patient anatomy and thus can improve the accuracy of medical procedures. Radius of curvature is an important parameter while designing steerable needles and achieving smaller radius and being able to control it is of paramount importance in steerable needle technology. We have developed a new class of steerable needles namely fracture-directed waterjet steerable needles in which the direction of the tissue fracture is controlled by waterjet and then the flexible needle follows. Needle steering tests are performed on soft tissue simulants, and the Radius of curvature of the needle is controlled by duty cycling of waterjet whereas 100% percent duty (waterjet is ON in all steps) gives the best radius of curvature. Smaller radius of curvature makes steering around tight obstacles possible and improves the performance of steerable needles. It is shown that the radius of curvature is a linear function of duty cycling for a range of the tissue stiffnesses used. A discrete-step kinematic model is used to model the motion of the waterjet steerable needle. This model consists of two parts: (1) the mechanics-based model predicts the cut-depth of waterjet in soft tissue based on soft tissue properties, waterjet diameter, and water exit velocity, and (2) a discrete-step kinematic unicycle model of the steerable needle travel. The proposed method of needle steering promises steerability and radius of curvature unattainable by current steerable needle technologies.