title: Comparison and evaluation of retrospective intermodality brain image registration techniques.
abstract: OBJECTIVE
  The primary objective of this study is to perform a blinded evaluation of a group of retrospective image registration techniques using as a gold standard a prospective, marker-based registration method. To ensure blindedness, all retrospective registrations were performed by participants who had no knowledge of the gold standard results until after their results had been submitted. A secondary goal of the project is to evaluate the importance of correcting geometrical distortion in MR images by comparing the retrospective registration error in the rectified images, i.e., those that have had the distortion correction applied, with that of the same images before rectification.
  
  
  METHODS
  Image volumes of three modalities (CT, MR, and PET) were obtained from patients undergoing neurosurgery at Vanderbilt University Medical Center on whom bone-implanted fiducial markers were mounted. These volumes had all traces of the markers removed and were provided via the Internet to project collaborators outside Vanderbilt, who then performed retrospective registrations on the volumes, calculating transformations from CT to MR and/ or from PET to MR. These investigators communicated their transformations again via the Internet to Vanderbilt, where the accuracy of each registration was evaluated. In this evaluation, the accuracy is measured at multiple volumes of interest (VOIs), i.e., areas in the brain that would commonly be areas of neurological interest. A VOI is defined in the MR image and its centroid c is determined. Then, the prospective registration is used to obtain the corresponding point c' in CT or PET. To this point, the retrospective registration is then applied, producing c" in MR. Statistics are gathered on the target registration error (TRE), which is the distance between the original point c and its corresponding point c".
  
  
  RESULTS
  This article presents statistics on the TRE calculated for each registration technique in this study and provides a brief description of each technique and an estimate of both preparation and execution time needed to perform the registration.
  
  
  CONCLUSIONS
  Our results indicate that retrospective techniques have the potential to produce satisfactory results much of the time, but that visual inspection is necessary to guard against large errors.
authors.affiliation: Department of Computer Science, Vanderbilt University, Nashville, TN 37235, USA.
authors.forename: J
authors.initials: J
authors.lastname: West
authors.forename: J M
authors.initials: JM
authors.lastname: Fitzpatrick
authors.forename: M Y
authors.initials: MY
authors.lastname: Wang
authors.forename: B M
authors.initials: BM
authors.lastname: Dawant
authors.forename: C R
authors.initials: CR
authors.lastname: Maurer
authors.forename: R M
authors.initials: RM
authors.lastname: Kessler
authors.forename: R J
authors.initials: RJ
authors.lastname: Maciunas
authors.forename: C
authors.initials: C
authors.lastname: Barillot
authors.forename: D
authors.initials: D
authors.lastname: Lemoine
authors.forename: A
authors.initials: A
authors.lastname: Collignon
authors.forename: F
authors.initials: F
authors.lastname: Maes
authors.forename: P
authors.initials: P
authors.lastname: Suetens
authors.forename: D
authors.initials: D
authors.lastname: Vandermeulen
authors.forename: P A
authors.initials: PA
authors.lastname: van den Elsen
authors.forename: S
authors.initials: S
authors.lastname: Napel
authors.forename: T S
authors.initials: TS
authors.lastname: Sumanaweera
authors.forename: B
authors.initials: B
authors.lastname: Harkness
authors.forename: P F
authors.initials: PF
authors.lastname: Hemler
authors.forename: D L
authors.initials: DL
authors.lastname: Hill
authors.forename: D J
authors.initials: DJ
authors.lastname: Hawkes
authors.forename: C
authors.initials: C
authors.lastname: Studholme
authors.forename: J B
authors.initials: JB
authors.lastname: Maintz
authors.forename: M A
authors.initials: MA
authors.lastname: Viergever
authors.forename: G
authors.initials: G
authors.lastname: Malandain
authors.forename: R P
authors.initials: RP
authors.lastname: Woods
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology*; D003195:Computer Communication Networks; D003951:Diagnostic Errors; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D015588:Observer Variation; D011446:Prospective Studies; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D019112:Teleradiology / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D014055:Tomography, Emission-Computed / Q000295:instrumentation / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data