title: Deformation vector fields (DVF)-driven image reconstruction for 4D-CBCT.
abstract: BACKGROUND
  High quality 4D-CBCT can be obtained by deforming a planning CT (pCT), where the deformation vector fields (DVF) are estimated by matching the forward projections of pCT and 4D-CBCT projections. The matching metric used in the previous study is the sum of squared intensity differences (SSID). The scatter signal level in CBCT projections is much higher than pCT, the SSID metric may not lead to optimal DVF.
  
  
  OBJECTIVE
  To improve the DVF estimation accuracy, we develop a new matching metric that is less sensitive to the intensity level difference caused by the scatter signal.
  
  
  METHODS
  The negative logarithm of correlation coefficient (NLCC) is used as the matching metric. A non-linear conjugate gradient optimization algorithm is used to estimate the DVF. A 4D NCAT phantom and an anthropomorphic thoracic phantom were used to evaluate the NLCC-based algorithm.
  
  
  RESULTS
  In the NCAT phantom study, the relative reconstruction error is reduced from 18.0% in SSID to 14.13% in NLCC. In the thoracic phantom study, the root mean square error of the tumor motion is reduced from 1.16 mm in SSID to 0.43 mm in NLCC.
  
  
  CONCLUSIONS
  NLCC metric can improve the image reconstruction and motion estimation accuracy of DVF-driven image reconstruction for 4D-CBCT.
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Dang
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Ouyang
authors.initials: O
authors.lastname: Luo
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Xuejun
authors.initials: X
authors.lastname: Gu
authors.affiliation: Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D056973:Four-Dimensional Computed Tomography / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D009716:Numerical Analysis, Computer-Assisted; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging*
keywords: 4D-CBCT; DVF estimation from projection; DVF-driven image reconstruction