An Integrator-Backstepping Control Approach For Out-of-Plane Needle Deflection Minimization
In this paper, we develop a needle steering strategy designed to reduce the out-of-plane deflection of a flexible, bevel-tipped needle. This is performed through an integrator backstepping approach. Integrator-backstepping is a nonlinear feedback controller design that divides the entire system into a sequence of smaller design problems that are easier to manage. Simulations were performed to observe the effects of our controller design on the system’s response, specifically the rate at which the out-of-plane deflection can be stabilized. We tested our proposed method using a biological tissue phantom composed of two separate heterogeneous layers and using an 18 gauge brachytherapy needle. A paired-sample t-test was performed to compare out-of-plane needle deflection results with and without the use of our needle steering algorithm under varying bevel-angle starting conditions. Results showed a significant decrease in the out-of-plane needle deflection with the use of our controller at the 1% significance level. The absolute-mean out-of-plane needle deflection at a depth of 140 mm changed from 7.1 mm to 0.7 mm with the implementation of our needle steering approach. Our proposed steering method does not require "drilling" motions often encountered in duty cycling controllers, and has been shown to be effective for clinical needles travelling through multiple heterogeneous tissue layers.