title: Fluoroscopy-based laser guidance system for linear surgical tool insertion depth control.
abstract: OBJECTIVE
  In most orthopedic surgeries, knowing how far to insert surgical tools is crucial. The objective of this study was to provide guidance information on depth without tracking surgical tools. A previously developed laser guidance system for linear surgical tool insertion uses two laser beams that display the insertion point and orientation on the skin surface. However, the system only provides 4 degrees of freedom guidance (an entry point on the planned pathway line and the orientation) but do not inform surgeons on the ideal insertion depth.
  
  
  METHODS
  A 5-DOF guidance method was developed to provide guidance information by direct projection onto the surgical area using laser beams without tracking markers. A position and orientation guidance performed by two laser beams and depth guidance performed by a single laser beam are appeared on the surgical area in turn. However, depth point appears on the surgical tool side face with some error because of tool radius. Using the actual depth position, insertion path vector and location of the laser sources, the correct depth point on the tool's surface is calculated by the proposed method. So, this system can indicate and navigate the 5-DOF which is planning path and the correct depth point.
  
  
  RESULTS
  An evaluation of the accuracy of depth guidance revealed a depth guidance error of 0.55±0.29 mm and results from phantom target insertions revealed overall system accuracies of 1.44 ± 1.09 mm, 0.91° ± 0.82°. In addition, overall system accuracies of application feasibility experiment under the X-ray condition were 1.94 ± 0.98mm, 1.39° ± 1.30°.
  
  
  CONCLUSIONS
  A new surgical tool depth insertion method was developed using a fluorolaser guidance system. This tool informs surgeons of the surgical tool tip depth assuming that the insertion point and orientation are correct. The new method was tested successfully in vitro.
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Room # 307, Takeda Sentanchi Building, Yayoi 2-11-16, Bunkyo, Tokyo, 113-8656, Japan, doke@image.t.u-tokyo.ac.jp.
authors.forename: Takehito
authors.initials: T
authors.lastname: Doke
authors.forename: Jack T
authors.initials: JT
authors.lastname: Liang
authors.forename: Shinya
authors.initials: S
authors.lastname: Onogi
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Nakajima
mesh_terms: D004867:Equipment Design; D005471:Fluoroscopy / Q000295:instrumentation*; D006801:Humans; D053685:Laser Therapy / Q000295:instrumentation*; D007834:Lasers; D019047:Phantoms, Imaging; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*