Design And Control Of An Ultrasound-guided Needle Insertion Robotic System On The Liver Tumor

Radioactive seed implantation is an effective invasive treatment for malignant tumors and has been attracting more and more attention from various research groups recently.It can release low-dosage X-ray and increase the dosage distribution ratio between locally radioactive tissues and normal tissues,which make the treatment safer and relieving short-term pain of patients.However,the efficacy of the technique relies on the precision of needle placement,which depends on the surgeons’ experience.To reduce the radiation exposure of medical staff as well as increase and stablize the implantation accuracy,this thesis proposes a surgical robotic system for brachytherapy on the liver tumor.The main topics of the thesis is as follows:(1)Mechanical design of the robotic system This thesis first discusses the workflow of robot-assisted brachytherapy as well as the design requirement.According to the requirement,a 5 DoF robotic system is designed,where 3 DoF is for translation and 2 DoF is for revolution.The system is equipped with an ultrasound scanner,force sensor and optical tracking system,which can provide ultrasound image,the axial force of needle and special position of the end effector,respectively.(2)Design of motion control strategyConsidering the collision and rubbing between the probe and the skin,this thesis presents a motion control strategy according to the system.The strategy is comprised of an artificial-potential-field-based path planning method and an ultrasound-image-based contact detecting method.With the methods,the system can perform obstacle-avoiding path planning and safe contact between the probe and the skin automatically.(3)Experiments and evaluation of the system and the method This thesis conducts several experiments to evaluate the performance of the system and the proposed methods.Results show that the mean of positioning error is 0.69 mm and the standard deviation is 0.33 mm.The result of the motion control experiment demonstrates the feasibility of the control strategy.Besides,the analysis of needle insertion force is also presented by an example experiment.