Percutaneous interventions involving the insertion of needles to anatomic targets within the body are applied in the diagnosis and treatment of many diseases. Robotic needle steering, a technique for inserting flexible needles along curved paths through tissue, has the potential to improve a variety of these percutaneous interventions. In our focus application, percutaneous radiofrequency ablation (RFA) of liver tumors, robotic systems can potentially allow clinicians to steer needles around obstacles to reach previously unattainable regions, treat multiple lesions with a single capsule wound, and treat large lesions with precise ablations of arbitrary shape.
An important obstacle to the adoption of needle steering in our target application is the limited curvature achieved by existing steerable needles in liver tissue. In our prior work, we performed a workspace analysis of needle steering in the liver, and found that radius of curvature below 50 mm is required to reach tumors located throughout the organ. Relevant existing needle steering techniques have been shown to achieve radius of curvature between 137 mm and 400 mm.
In this paper, the impact of tip geometry on steerable needle curvature is examined. Finite-element simulations and experiments with bent-tip needles in ex vivo liver tissue demonstrate that selection of tip length and angle can greatly improve curvature, with radius of curvature below 50 mm in liver tissue possible through judicious selection of these parameters. Motivated by the results of this analysis, a new articulated-tip steerable needle is described, in which a distal section is actively switched between straight and bent configurations. Validation testing shows the new articulated-tip needle achieves smaller radius of curvature compared to bent-tip needles described in previous work. Steerable needles with optimized tip parameters, which can generate tight curves in liver tissue, increase the clinical relevance of needle steering to percutaneous interventions.
Keywords: Robotic needle steering, flexible needles, medical robots, percutaneous interventions