Needle Steering via External Forces on the Tissue

Meysam Torabi, Rik Jansen, Kris Hauser, Ron Alterovitz, Vincent Duindam, and Ken Goldberg

The goal of this project is to demonstrate that by applying appropriate forces at specific external points on the tissue, some previously unreachable targets can be hit by medical needles. From a modeling point of view, this external manipulation can be considered as a new input for robotic needle steering systems.

The needle steering is divided into 4 steps from the beginning until the needle hits the target. In each step, a specific velocity is assigned to the needle in order to control the manipulation of the target and obstacles and also to decrease tissue deformation. The needle is assumed to be rigid and as a result, the external manipulation can not bend the needle shaft and hence the needle acts as a boundary. The tissue is modeled using the Finite Element Method (FEM) considering the effect of penetration velocity on the amount of tissue deformation. The external manipulation is modeled by applying varying forces on the selected external nodes determined by optimization. The environment is highly interactive between three elements: needle, tissue and external manipulations, each of which affects the others (Fig 1).

The planning and optimization determine which edge, how many nodes and which nodes should be manipulated so that the target and obstacles can be appropriately repositioned to the optimal points. The optimizer also determines the best insertion point so that the needle, after applying the manipulations, can hit the target without any collision with the obstacles. Since the plant behavior is very coupled between the competing objectives, a closed-loop system equipped with a visual feedback is designed to regularly scan the environment. The feedback is used to compensate for any unpredicted and/or unpredictable disturbances attacking the plant. The controller, placed in the forward path of the loop, is a carefully tuned PI/P controller which, in each step of the simulation, calculates specific amount of the external forces (Fig 1). Also, the controller determines when the forces should be applied and then, when they should be removed from the tissue. The external manipulations continue until the distance between the needle body and the obstacles is maximized and also the target is stably placed in front of the needle tip. In order to enable a user to perform interactive tasks and design a desired environment, a Graphical User Interface (GUI) is designed (Fig 2). Then, the planner and controllers are adaptively able to safely steer the needle to the target in any case imported by GUI.

As the future work, we intend to extend this method on a 3D FEM-based multi-layer non-homogenous tissue with multiple targets and different-shape obstacles. Another interesting topic in this area is that how to periodically manipulate different points of a tissue during a surgery, in order to compensate tissue beating and dynamically stabilize the tissue. This compensation can ease needle steering in beating tissues by increasing targeting accuracy.

Fig 1. Simulation of a prostate brachytherapy procedure with external manipulation. A manipulator in the rectum (blue) shifts sensistive tissues away from the needle path.

Fig 2. External manipulation from above guides the needle between the obstacles, and manipulation from below ensure accurate targeting.