title: How accurate are the fusion of cone-beam CT and 3-D stereophotographic images?
abstract: BACKGROUND
  Cone-beam Computed Tomography (CBCT) and stereophotography are two of the latest imaging modalities available for three-dimensional (3-D) visualization of craniofacial structures. However, CBCT provides only limited information on surface texture. This can be overcome by combining the bone images derived from CBCT with 3-D photographs. The objectives of this study were 1) to evaluate the feasibility of integrating 3-D Photos and CBCT images 2) to assess degree of error that may occur during the above processes and 3) to identify facial regions that would be most appropriate for 3-D image registration.
  
  
  METHODS
  CBCT scans and stereophotographic images from 29 patients were used for this study. Two 3-D images corresponding to the skin and bone were extracted from the CBCT data. The 3-D photo was superimposed on the CBCT skin image using relatively immobile areas of the face as a reference. 3-D colour maps were used to assess the accuracy of superimposition were distance differences between the CBCT and 3-D photo were recorded as the signed average and the Root Mean Square (RMS) error.
  
  
  RESULTS
  The signed average and RMS of the distance differences between the registered surfaces were -0.018 (±0.129) mm and 0.739 (±0.239) mm respectively. The most errors were found in areas surrounding the lips and the eyes, while minimal errors were noted in the forehead, root of the nose and zygoma.
  
  
  CONCLUSIONS
  CBCT and 3-D photographic data can be successfully fused with minimal errors. When compared to RMS, the signed average was found to under-represent the registration error. The virtual 3-D composite craniofacial models permit concurrent assessment of bone and soft tissues during diagnosis and treatment planning.
authors.affiliation: Discipline of Oral & Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, Hong Kong, Hong Kong SAR.
authors.forename: Yasas S N
authors.initials: YS
authors.lastname: Jayaratne
authors.forename: Colman P J
authors.initials: CP
authors.lastname: McGrath
authors.forename: Roger A
authors.initials: RA
authors.lastname: Zwahlen
mesh_terms: D000465:Algorithms; D001842:Bone and Bones / Q000473:pathology*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003952:Diagnostic Imaging / Q000379:methods; D001330:Electronic Data Processing; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D015233:Models, Statistical; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D012867:Skin / Q000473:pathology*; D012984:Software