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Sliding Mode Control System for Steerable Needles
A team of Vanderbilt engineers has developed an advanced control system that is a first-ever 3D control system for delivering a bevel-based steerable needle to its intended target. The controller is also useful for (a) following a desired curved path through tissue; (b) accurately placing the needle tip at the physician’s desired target, and (c) reaching obstructed targets using non-straight paths. Experiments in phantom tissue and ex-vivo liver have validated the concept. Experiments with targets that move due to tissue deformation have also been successful.
Addressed Clinical Need
Millions of procedures are performed every year with needles for biopsy, thermal ablation, brachytherapy, and drug delivery, among others. For example, it is estimated that annually there are 1.6 million breast biopsies in United States and 1 million prostate biopsies worldwide. Efficacy of these needle-based procedures is often compromised due to needle placement inaccuracy, tissue deformation, registration error, and the surgeon’s hand–eye coordination. All of the procedures depend on the accurate control of the needle tip with respect to information from medical images. The potential to address accuracy enhancement has led to a growing interest in steerable needles in interventional medicine.
Challenges with Current Steerable Needles
At the present time, the primary constraints in the application of steerable needles lies in (a) the limitation of a straight-line approach, and (b) the inaccuracy involved in placement of steerable needles to the specific location of interest. The curved trajectories demonstrated by steerable needles (as shown in Figure 1) make it clear that they can address the first constraint with conventional needle placement. However, until now there has been no good way to control these needles to reach a desired point. This second constraint is overcome by the use of a sliding mode controller that automatically adjusts needle axial rotation during insertion to steer the needle toward the desired target. The new controller is simple to implement, works directly using 3D information, and is provably convergent.
The full details of this control approach and its performance are given in the paper cited below. In summary, the control law continually updates the insertion speed and the speed of axial rotation (clockwise or counter clockwise) at the needle base as a function of the target position relative to the tip of the needle. In basic intuitive terms, this approach always rotates the needle towards a state in which it naturally curves towards the target while respecting desired limits on insertion and rotation speed. Further modifications to this basic approach enable the needle to track desired trajectories through tissue, and limit the total rotation of the needle base. The new controller is simple to implement, works directly using 3D information, and is provably convergent. As shown in Figure 2, experiments on phantom targets and liver tissue shows accurate delivery of the needle tip to the desired target.
Development and Intellectual Property Status
The control system has been built and experimentally demonstrated at Vanderbilt.
A Patent Application has been filed
Lab home Page with list of publications and ongoing research portfolio: http://research.vuse.vanderbilt.edu/medlab/index.htm