Investigation of tool-tissue interactions for application to surgical needle insertion

Abstract

Needle insertions are performed for a variety of medical diagnostic and therapeutic procedures, where placement accuracy has a direct influence on the effectiveness and potential injury associated to a given treatment. However, interventions in soft tissues are challenging due to the deforming anatomy, restricted view of the surgical area and restricted control of the surgical instruments. Steerable surgical needles can assist surgeons to access deep-seated targets with high accuracy, while avoiding obstacles and sensitive regions along the insertion path. One approach to this is provided by a biologically inspired needle, which is currently under development at Imperial College. The needle consists of four axially interlocked segments, enabling it to steer within a compliant medium, with bioinspired motion profiles that can result in reduced tissue deformation. This thesis aims to advance the development of this needle and to produce a better understanding of the tool-tissue interactions, which influence its ability to steer and its impact on the surrounding tissue. Experimental setups are developed for the insertion of rigid and flexible needles using tissue phantom materials and a laser based image correlation technique. For spatially resolved measurements of the material response close to the needle and at high resolution, micrometre-sized particles embedded in a tissue phantom are illuminated in a laser light sheet, and tracked using one or multiple cameras. From recorded images, displacements and strains are obtained inside the substrate to compare the extent of tissue disruption for different insertion methods. Using this technique, different phantom materials are assessed for realistic modelling of interactions, and different insertion motion profiles are evaluated to ascertain which parameters of the interaction influence needle performance. Finally, results of the deformation study and tool-tissue characterisation are employed to explore the effect of needle trajectories and insertion strategies on target motion. The thesis ends with conclusions and future work, drawn from the results on tissue phantoms, motion strategies and target motion, which can be used to improve existing models and to accelerate the development of steerable surgical tools, leading to safer and more accurate needle placement.