title: Noninvasive magnetic resonance to three-dimensional rotational x-ray registration of vertebral bodies for image-guided spine surgery.
abstract: METHODS
  Magnetic resonance (MR) and three-dimensional rotational x-ray (3DRX) images of cadaveric spinal segments were registered using a conventional point-based technique and a noninvasive technique called maximization of mutual information (MMI).
  
  
  OBJECTIVE
  To assess the feasibility and accuracy of MMI-based registration in comparison with point-based registration as a new noninvasive image-to-patient registration technique for use in minimally invasive image-guided spine surgery.
  
  
  BACKGROUND
  In image-guided orthopedic surgery, correspondence between before surgery acquired images and the patient is required. Currently, this necessitates an invasive registration step, in which anatomic landmarks on the bone surface have to be physically touched by a pointer. To overcome this invasive procedure, we propose using a calibrated 3DRX system, a modality that can visualize high contrast objects intraoperatively and that provides a direct correspondence between the image data and the patient. A noninvasive voxel-based technique is used to register the intraoperative 3DRX image to a before surgery acquired MR image.
  
  
  METHODS
  Cadaveric thoracic and lumbar spine segments were implanted with markers, which were used as landmarks. The accuracy of the landmark-based registration was compared with MMI-based registration using the residual errors on the marker positions.
  
  
  RESULTS
  The errors made using the point-based registration technique were compared with the errors made with MMI. The results show a statistically significant lower error (P < 0.01) for the proposed MMI method.
  
  
  CONCLUSIONS
  Noninvasive MMI registration of intraoperative 3DRX images to preoperative MR images is more accurate than point-based registration in cadaveric spine segments. It is therefore a promising technique for replacing the invasive landmark-based registration that is currently used in image-guided spine surgery.
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands. everine@isi.uu.nl
authors.forename: Everine B
authors.initials: EB
authors.lastname: van de Kraats
authors.forename: Theo
authors.initials: T
authors.lastname: van Walsum
authors.forename: Jorrit-Jan
authors.initials: JJ
authors.lastname: Verlaan
authors.forename: F Cumhur
authors.initials: FC
authors.lastname: Oner
authors.forename: Max A
authors.initials: MA
authors.lastname: Viergever
authors.forename: Wiro J
authors.initials: WJ
authors.lastname: Niessen
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D019637:Orthopedic Procedures; D013131:Spine / Q000000981:diagnostic imaging* / Q000601:surgery*; D025321:Surgery, Computer-Assisted; D014057:Tomography, X-Ray Computed