Kinematics modelling and dynamics analysis of an SMA-actuated active flexible needle for feedback-controlled manipulation in phantom.

Percutaneous needle-based procedures such as prostate brachytherapy demands for accurate placement of the needle tip at target locations. Recently, robotic needle insertion systems have been made available to help physicians in needle guidance and control inside tissue. It is often challenging to obtain an accurate and real-time position of the needle tip in clinical practice using medical imaging techniques. However, this information is vital for closed-loop control of the needles inside tissue. This work presents an SMA-actuated active flexible needle that is controlled inside a phantom without a need for a position sensor or a medical imaging device. The needle tip position feedback is found using shape sensing capabilities of the embedded SMA-wire actuators and a force sensor at the needle base. Three models were characterized and used to estimate needle tip position in real time. The control scheme was then tested on the active flexible needle to track a desired triangular trajectory in a phantom. It was shown that the control scheme presented in this work was able to manipulate the needle in this path with a reasonable accuracy.