title: Three-dimensional ultrasound image-guided robotic system for accurate microwave coagulation of malignant liver tumours.
abstract: BACKGROUND
  The further application of conventional ultrasound (US) image-guided microwave (MW) ablation of liver cancer is often limited by two-dimensional (2D) imaging, inaccurate needle placement and the resulting skill requirement. The three-dimensional (3D) image-guided robotic-assisted system provides an appealing alternative option, enabling the physician to perform consistent, accurate therapy with improved treatment effectiveness.
  
  
  METHODS
  Our robotic system is constructed by integrating an imaging module, a needle-driven robot, a MW thermal field simulation module, and surgical navigation software in a practical and user-friendly manner. The robot executes precise needle placement based on the 3D model reconstructed from freehand-tracked 2D B-scans. A qualitative slice guidance method for fine registration is introduced to reduce the placement error caused by target motion. By incorporating the 3D MW specific absorption rate (SAR) model into the heat transfer equation, the MW thermal field simulation module determines the MW power level and the coagulation time for improved ablation therapy. Two types of wrists are developed for the robot: a 'remote centre of motion' (RCM) wrist and a non-RCM wrist, which is preferred in real applications.
  
  
  RESULTS
  The needle placement accuracies were < 3 mm for both wrists in the mechanical phantom experiment. The target accuracy for the robot with the RCM wrist was improved to 1.6 +/- 1.0 mm when real-time 2D US feedback was used in the artificial-tissue phantom experiment. By using the slice guidance method, the robot with the non-RCM wrist achieved accuracy of 1.8 +/- 0.9 mm in the ex vivo experiment; even target motion was introduced. In the thermal field experiment, a 5.6% relative mean error was observed between the experimental coagulated neurosis volume and the simulation result.
  
  
  CONCLUSIONS
  The proposed robotic system holds promise to enhance the clinical performance of percutaneous MW ablation of malignant liver tumours.
authors.affiliation: Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48823, USA. xujing0829@gmail.com
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.forename: Zhen-zhong
authors.initials: ZZ
authors.lastname: Jia
authors.forename: Zhang-jun
authors.initials: ZJ
authors.lastname: Song
authors.forename: Xiang-dong
authors.initials: XD
authors.lastname: Yang
authors.forename: Ken
authors.initials: K
authors.lastname: Chen
authors.forename: Ping
authors.initials: P
authors.lastname: Liang
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015994:Incidence; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000401:mortality / Q000601:surgery*; D051379:Mice; D008872:Microwaves / Q000627:therapeutic use; D009339:Needles; D012371:Robotics / Q000295:instrumentation / Q000379:methods*; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D014465:Ultrasonics; D014463:Ultrasonography; D014481:United States