title: Filtered-backprojection reconstruction for a cone-beam computed tomography scanner with independent source and detector rotations.
abstract: OBJECTIVE
  A new cone-beam CT scanner for image-guided radiotherapy (IGRT) can independently rotate the source and the detector along circular trajectories. Existing reconstruction algorithms are not suitable for this scanning geometry. The authors propose and evaluate a three-dimensional (3D) filtered-backprojection reconstruction for this situation.
  
  
  METHODS
  The source and the detector trajectories are tuned to image a field-of-view (FOV) that is offset with respect to the center-of-rotation. The new reconstruction formula is derived from the Feldkamp algorithm and results in a similar three-step algorithm: projection weighting, ramp filtering, and weighted backprojection. Simulations of a Shepp Logan digital phantom were used to evaluate the new algorithm with a 10 cm-offset FOV. A real cone-beam CT image with an 8.5 cm-offset FOV was also obtained from projections of an anthropomorphic head phantom.
  
  
  RESULTS
  The quality of the cone-beam CT images reconstructed using the new algorithm was similar to those using the Feldkamp algorithm which is used in conventional cone-beam CT. The real image of the head phantom exhibited comparable image quality to that of existing systems.
  
  
  CONCLUSIONS
  The authors have proposed a 3D filtered-backprojection reconstruction for scanners with independent source and detector rotations that is practical and effective. This algorithm forms the basis for exploiting the scanner's unique capabilities in IGRT protocols.
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Department of Radiation Oncology, Centre Léon Bérard, 28 rue Laennec, Lyon 69008, France.
authors.forename: Simon
authors.initials: S
authors.lastname: Rit
authors.affiliation: Laboratoire Hubert Curien, CNRS and Université Jean Monnet (UMR5516), 18 rue du Professeur Benoit Lauras, Saint Etienne F-42000, France.
authors.forename: Rolf
authors.initials: R
authors.lastname: Clackdoyle
authors.affiliation: Institute for Research and Development on Advanced Radiation Technologies (radART), Paracelsus Medical University, Strubergasse 16, Salzburg 5020, Austria and medPhoton GmbH, Strubergasse 16, Salzburg 5020, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Keuschnigg
authors.affiliation: Institute for Research and Development on Advanced Radiation Technologies (radART), Paracelsus Medical University, Strubergasse 16, Salzburg 5020, Austria and medPhoton GmbH, Strubergasse 16, Salzburg 5020, Austria.
authors.forename: Philipp
authors.initials: P
authors.lastname: Steininger
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation* / Q000379:methods*; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods*; D008953:Models, Anatomic; D019047:Phantoms, Imaging; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods; D012399:Rotation