title: Reducing metal artifacts in cone-beam CT images by preprocessing projection data.
abstract: OBJECTIVE
  Computed tomography (CT) streak artifacts caused by metallic implants remain a challenge for the automatic processing of image data. The impact of metal artifacts in the soft-tissue region is magnified in cone-beam CT (CBCT), because the soft-tissue contrast is usually lower in CBCT images. The goal of this study was to develop an effective offline processing technique to minimize the effect.
  
  
  METHODS
  The geometry calibration cue of the CBCT system was used to track the position of the metal object in projection views. The three-dimensional (3D) representation of the object can be established from only two user-selected viewing angles. The position of the shadowed region in other views can be tracked by projecting the 3D coordinates of the object. Automatic image segmentation was used followed by a Laplacian diffusion method to replace the pixels inside the metal object with the boundary pixels. The modified projection data were then used to reconstruct a new CBCT image. The procedure was tested in phantoms, prostate cancer patients with implanted gold markers and metal prosthesis, and a head-and-neck patient with dental amalgam in the teeth.
  
  
  RESULTS
  Both phantom and patient studies demonstrated that the procedure was able to minimize the metal artifacts. Soft-tissue visibility was improved near or away from the metal object. The processing time was 1-2 s per projection.
  
  
  CONCLUSIONS
  We have implemented an effective metal artifact-suppressing algorithm to improve the quality of CBCT images.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Yongbin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Lifei
authors.initials: L
authors.lastname: Zhang
authors.forename: X Ronald
authors.initials: XR
authors.lastname: Zhu
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lee
authors.forename: Mark
authors.initials: M
authors.lastname: Chambers
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
mesh_terms: D000465:Algorithms; D016477:Artifacts; D002138:Calibration; D003723:Dental Amalgam; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D006801:Humans; D008297:Male; D008670:Metals; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D019736:Prostheses and Implants; D011856:Radiographic Image Enhancement / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed
chemical_list: D008670:Metals; D003723:Dental Amalgam