title: Robust initialization of 2D-3D image registration using the projection-slice theorem and phase correlation.
abstract: OBJECTIVE
  The image registration literature comprises many methods for 2D-3D registration for which accuracy has been established in a variety of applications. However, clinical application is limited by a small capture range. Initial offsets outside the capture range of a registration method will not converge to a successful registration. Previously reported capture ranges, defined as the 95% success range, are in the order of 4-11 mm mean target registration error. In this article, a relatively computationally inexpensive and robust estimation method is proposed with the objective to enlarge the capture range.
  
  
  METHODS
  The method uses the projection-slice theorem in combination with phase correlation in order to estimate the transform parameters, which provides an initialization of the subsequent registration procedure.
  
  
  RESULTS
  The feasibility of the method was evaluated by experiments using digitally reconstructed radiographs generated from in vivo 3D-RX data. With these experiments it was shown that the projection-slice theorem provides successful estimates of the rotational transform parameters for perspective projections and in case of translational offsets. The method was further tested on ex vivo ovine x-ray data. In 95% of the cases, the method yielded successful estimates for initial mean target registration errors up to 19.5 mm. Finally, the method was evaluated as an initialization method for an intensity-based 2D-3D registration method. The uninitialized and initialized registration experiments had success rates of 28.8% and 68.6%, respectively.
  
  
  CONCLUSIONS
  The authors have shown that the initialization method based on the projection-slice theorem and phase correlation yields adequate initializations for existing registration methods, thereby substantially enlarging the capture range of these methods.
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, QOS.459, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. m.vanderbom@umcutrecht.nl
authors.forename: M J
authors.initials: MJ
authors.lastname: van der Bom
authors.forename: L W
authors.initials: LW
authors.lastname: Bartels
authors.forename: M J
authors.initials: MJ
authors.lastname: Gounis
authors.forename: R
authors.initials: R
authors.lastname: Homan
authors.forename: J
authors.initials: J
authors.lastname: Timmer
authors.forename: M A
authors.initials: MA
authors.lastname: Viergever
authors.forename: J P W
authors.initials: JP
authors.lastname: Pluim
mesh_terms: D000465:Algorithms; D000818:Animals; D019540:Area Under Curve; D004285:Dogs; D004867:Equipment Design; D005583:Fourier Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods; D015233:Models, Statistical; D016011:Normal Distribution; D011859:Radiography / Q000379:methods; D015203:Reproducibility of Results; D014965:X-Rays