title: MRI-compatible manipulator with remote-center-of-motion control.
abstract: OBJECTIVE
  To develop and assess a needle-guiding manipulator for MRI-guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site.
  
  
  METHODS
  The manipulator consists of a three-degrees-of-freedom (DOF) base stage and passive needle holder with unconstrained two-DOF rotation. The synergistic control keeps the Virtual RCM at the preplanned target using encoder outputs from the needle holder as input to motorize the base stage.
  
  
  RESULTS
  The manipulator assists in searching for an optimal needle insertion path which is a complex and time-consuming task in MRI-guided ablation therapy for liver tumors. The assessment study showed that accuracy of keeping the virtual RCM to predefined position is 3.0 mm. In a phantom test, the physicians found the needle insertion path faster with than without the manipulator (number of physicians = 3, P = 0.001). However, the alignment time with the virtual RCM was not shorter when imaging time for planning were considered.
  
  
  CONCLUSIONS
  The study indicated that the robot holds promise as a tool for accurately and interactively selecting the optimal needle insertion path in liver ablation therapy guided by open-configuration MRI.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts 02115, USA. hata@bwh.harvard.edu
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Hata
authors.forename: Junichi
authors.initials: J
authors.lastname: Tokuda
authors.forename: Shelley
authors.initials: S
authors.lastname: Hurwitz
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Morikawa
mesh_terms: D000465:Algorithms; D017115:Catheter Ablation / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D008113:Liver Neoplasms / Q000601:surgery*; D053783:Magnetic Resonance Imaging, Interventional / Q000295:instrumentation*; D009339:Needles; D019047:Phantoms, Imaging