title: MIND Demons for MR-to-CT Deformable Image Registration In Image-Guided Spine Surgery.
abstract: OBJECTIVE
  Localization of target anatomy and critical structures defined in preoperative MR images can be achieved by means of multi-modality deformable registration to intraoperative CT. We propose a symmetric diffeomorphic deformable registration algorithm incorporating a modality independent neighborhood descriptor (MIND) and a robust Huber metric for MR-to-CT registration.
  
  
  METHODS
  The method, called MIND Demons, solves for the deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the velocity fields and the diffeomorphisms, a modality-insensitive similarity function suitable to multi-modality images, and constraints on geodesics in Lagrangian coordinates. Direct optimization (without relying on an exponential map of stationary velocity fields used in conventional diffeomorphic Demons) is carried out using a Gauss-Newton method for fast convergence. Registration performance and sensitivity to registration parameters were analyzed in simulation, in phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to conventional mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, and normalized MI (NMI) Demons.
  
  
  RESULTS
  The method yielded sub-voxel invertibility (0.006 mm) and nonsingular spatial Jacobians with capability to preserve local orientation and topology. It demonstrated improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.5 mm compared to 10.9, 2.3, and 4.6 mm for MI FFD, LMI FFD, and NMI Demons methods, respectively. Validation in clinical studies demonstrated realistic deformation with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine.
  
  
  CONCLUSIONS
  A modality-independent deformable registration method has been developed to estimate a viscoelastic diffeomorphic map between preoperative MR and intraoperative CT. The method yields registration accuracy suitable to application in image-guided spine surgery across a broad range of anatomical sites and modes of deformation.
authors.affiliation: Department of Computer Science, Johns Hopkins University, Baltimore MD.
authors.forename: S
authors.initials: S
authors.lastname: Reaungamornrat
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors.forename: T
authors.initials: T
authors.lastname: De Silva
authors.affiliation: Department of Computer Science, Johns Hopkins University, Baltimore MD.
authors.forename: A
authors.initials: A
authors.lastname: Uneri
authors.affiliation: Department of Neurosurgery - Spine, Johns Hopkins Hospital, Baltimore, MD.
authors.forename: J-P
authors.initials: JP
authors.lastname: Wolinsky
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD; Department of Orthopaedic Surgery, Johns Hopkins Health Care and Surgery Center, Bethesda, MD.
authors.forename: A J
authors.initials: AJ
authors.lastname: Khanna
authors.affiliation: Siemens Healthcare XP Division, Erlangen, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Kleinszig
authors.affiliation: Siemens Healthcare XP Division, Erlangen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Vogt
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD; Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore MD.
authors.forename: J L
authors.initials: JL
authors.lastname: Prince
authors.affiliation: Department of Computer Science, Johns Hopkins University, Baltimore MD; Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD.
authors.forename: J H
authors.initials: JH
authors.lastname: Siewerdsen
keywords: CT; Demons algorithm; MIND; MRI; deformable image registration; image-guided surgery; multimodality image registration; symmetric diffeomorphism