title: Intraoperative CT as a registration benchmark for intervertebral motion compensation in image-guided open spinal surgery.
abstract: OBJECTIVE
  An accurate and reliable benchmark of registration accuracy and intervertebral motion compensation is important for spinal image guidance. In this study, we evaluated the utility of intraoperative CT (iCT) in place of bone-implanted screws as the ground-truth registration and illustrated its use to benchmark the performance of intraoperative stereovision (iSV).
  
  
  METHODS
  A template-based, multi-body registration scheme was developed to individually segment and pair corresponding vertebrae between preoperative CT and iCT of the spine. Intervertebral motion was determined from the resulting vertebral pair-wise registrations. The accuracy of the image-driven registration was evaluated using surface-to-surface distance error (SDE) based on segmented bony features and was independently verified using point-to-point target registration error (TRE) computed from bone-implanted mini-screws. Both SDE and TRE were used to assess the compensation accuracy using iSV.
  
  
  RESULTS
  The iCT-based technique was evaluated on four explanted porcine spines (20 vertebral pairs) with artificially induced motion. We report a registration accuracy of 0.57 [Formula: see text] 0.32 mm (range 0.34-1.14 mm) and 0.29 [Formula: see text] 0.15 mm (range 0.14-0.78 mm) in SDE and TRE, respectively, for all vertebrae pooled, with an average intervertebral rotation of [Formula: see text] (range 1.5[Formula: see text]-7.9[Formula: see text]). The iSV-based compensation accuracy for one sample (four vertebrae) was 1.32 [Formula: see text] 0.19 mm and 1.72 [Formula: see text] 0.55 mm in SDE and TRE, respectively, exceeding the recommended accuracy of 2 mm.
  
  
  CONCLUSIONS
  This study demonstrates the effectiveness of iCT in place of invasive fiducials as a registration ground truth. These findings are important for future development of on-demand spinal image guidance using radiation-free images such as stereovision and ultrasound on human subjects.
authors.affiliation: Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA. Songbai.Ji@Dartmouth.edu.|Geisel School of Medicine, Dartmouth College, Hanover, NH, 03755, USA. Songbai.Ji@Dartmouth.edu.
authors.forename: Songbai
authors.initials: S
authors.lastname: Ji
authors.affiliation: Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA.
authors.forename: Xiaoyao
authors.initials: X
authors.lastname: Fan
authors.affiliation: Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA.|Dartmouth Hitchcock Medical Center, Lebanon, NH, 03766, USA.
authors.forename: Keith D
authors.initials: KD
authors.lastname: Paulsen
authors.affiliation: Geisel School of Medicine, Dartmouth College, Hanover, NH, 03755, USA.|Dartmouth Hitchcock Medical Center, Lebanon, NH, 03766, USA.
authors.forename: David W
authors.initials: DW
authors.lastname: Roberts
authors.affiliation: Geisel School of Medicine, Dartmouth College, Hanover, NH, 03755, USA.|Dartmouth Hitchcock Medical Center, Lebanon, NH, 03766, USA.
authors.forename: Sohail K
authors.initials: SK
authors.lastname: Mirza
authors.affiliation: Geisel School of Medicine, Dartmouth College, Hanover, NH, 03755, USA.|Dartmouth Hitchcock Medical Center, Lebanon, NH, 03766, USA.
authors.forename: S Scott
authors.initials: SS
authors.lastname: Lollis
mesh_terms: D000818:Animals; D019985:Benchmarking; D001863:Bone Screws; D004195:Disease Models, Animal; D005260:Female; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D009038:Motion; D009068:Movement; D013124:Spinal Injuries / Q000601:surgery; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Fusion surgery; Intervertebral motion; Intraoperative CT; Motion compensation; Patient registration; Registration accuracy; Spinal surgery