title: Autoadaptive phase-correlated (AAPC) reconstruction for 4D CBCT.
abstract: OBJECTIVE
  Kilovoltage cone-beam computed tomography (CBCT) is widely used in image-guided radiation therapy for exact patient positioning prior to the treatment. However, producing time series of volumetric images (4D CBCT) of moving anatomical structures remains challenging. The presented work introduces a novel method, combining high temporal resolution inside anatomical regions with strong motion and image quality improvement in regions with little motion.
  
  
  METHODS
  In the proposed method, the projections are divided into regions that are subject to motion and regions at rest. The latter ones will be shared among phase bins, leading thus to an overall reduction in artifacts and noise. An algorithm based on the concept of optical flow was developed to analyze motion-induced changes between projections. The technique was optimized to distinguish patient motion and motion deriving from gantry rotation. The effectiveness of the method is shown in numerical simulations and patient data.
  
  
  RESULTS
  The images reconstructed from the presented method yield an almost the same temporal resolution in the moving volume segments as a conventional phase-correlated reconstruction, while reducing the noise in the motionless regions down to the level of a standard reconstruction without phase correlation. The proposed simple motion segmentation scheme is yet limited to rotation speeds of less than 3 degrees/s.
  
  
  CONCLUSIONS
  The method reduces the noise in the reconstruction and increases the image quality. More data are introduced for each phase-correlated reconstruction, and therefore the applied dose is used more efficiently.
authors.affiliation: Institute of Medical Physics, University of Erlangen-Nürnberg, Erlangen D-91052, Germany. frank.bergner@imp.uni-erlangen.de
authors.forename: Frank
authors.initials: F
authors.lastname: Bergner
authors.forename: Timo
authors.initials: T
authors.lastname: Berkus
authors.forename: Markus
authors.initials: M
authors.lastname: Oelhafen
authors.forename: Patrik
authors.initials: P
authors.lastname: Kunz
authors.forename: Tinsu
authors.initials: T
authors.lastname: Pan
authors.forename: Marc
authors.initials: M
authors.lastname: Kachelriess
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results