title: Fiducial point placement and the accuracy of point-based, rigid body registration.
abstract: OBJECTIVE
  To demonstrate that the shape of the configuration of fiducial points is an important factor governing target registration error (TRE) in point-based, rigid registration.
  
  
  METHODS
  We consider two clinical situations: cranial neurosurgery and pedicle screw placement. For cranial neurosurgery, we apply theoretical results concerning TRE prediction, which we have previously derived and validated, to three hypothetical fiducial marker configurations. We illustrate the profile of expected TRE for each configuration. For pedicle screw placement, we apply the same theory to a common anatomic landmark configuration (tips of spinous and transverse processes) used for pedicle screw placement, and we estimate the error rate expected in placement of the screw.
  
  
  RESULTS
  In the cranial neurosurgery example, we demonstrate that relatively small values of TRE may be achieved by using widely spread fiducial markers and/or placing the centroid of the markers near the target. We also demonstrate that near-collinear marker configurations far from the target may result in large TRE values. In the pedicle screw placement example, we demonstrate that the screw must be approximately 4 mm narrower than the pedicle in which it is implanted to minimize the chance of pedicle violation during placement.
  
  
  CONCLUSIONS
  The placement of fiducial points is an important factor in minimizing the error rate for point-based, rigid registration. By using as many points as possible, avoiding near-collinear configurations, and ensuring that the centroid of the fiducial points is as near as possible to the target, TREs can be minimized.
authors.affiliation: Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: West
authors.forename: J M
authors.initials: JM
authors.lastname: Fitzpatrick
authors.forename: S A
authors.initials: SA
authors.lastname: Toms
authors.forename: C R
authors.initials: CR
authors.lastname: Maurer
authors.forename: R J
authors.initials: RJ
authors.lastname: Maciunas
mesh_terms: D001927:Brain Diseases / Q000601:surgery*; D003399:Craniotomy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion; D013238:Stereotaxic Techniques; D014584:User-Computer Interface