title: A new method to combine 3D reconstruction volumes for multiple parallel circular cone beam orbits.
abstract: OBJECTIVE
  This article presents a new reconstruction method for 3D imaging using a multiple 360 degrees circular orbit cone beam CT system, specifically a way to combine 3D volumes reconstructed with each orbit. The main goal is to improve the noise performance in the combined image while avoiding cone beam artifacts.
  
  
  METHODS
  The cone beam projection data of each orbit are reconstructed using the FDK algorithm. When at least a portion of the total volume can be reconstructed by more than one source, the proposed combination method combines these overlap regions using weighted averaging in frequency space. The local exactness and the noise performance of the combination method were tested with computer simulations of a Defrise phantom, a FORBILD head phantom, and uniform noise in the raw data.
  
  
  RESULTS
  A noiseless simulation showed that the local exactness of the reconstructed volume from the source with the smallest tilt angle was preserved in the combined image. A noise simulation demonstrated that the combination method improved the noise performance compared to a single orbit reconstruction.
  
  
  CONCLUSIONS
  In CT systems which have overlap volumes that can be reconstructed with data from more than one orbit and in which the spatial frequency content of each reconstruction can be calculated, the proposed method offers improved noise performance while keeping the local exactness of data from the source with the smallest tilt angle.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California 94305, USA. bjd1219@stanford.edu
authors.forename: Jongduk
authors.initials: J
authors.lastname: Baek
authors.forename: Norbert J
authors.initials: NJ
authors.lastname: Pelc
mesh_terms: D055592:Biophysical Phenomena; D054893:Cone-Beam Computed Tomography / Q000379:methods* / Q000706:statistics & numerical data; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods* / Q000706:statistics & numerical data; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*