title: Virtual reality for simulation of radiographic projections: validation of projection geometry.
abstract: OBJECTIVE
  To develop a software for virtual reality (VR) simulation of X-ray images based on perspective projections through a patient model derived from data from a CT examination and to evaluate the accuracy in the projection geometry obtained by the software.
  
  
  METHODS
  A VR software was developed on a personal computer, with models of a patient, an X-ray machine and a detector. The model of the patient was derived from data from a CT examination of a dry skull. Simulated radiographic images of the patient model could be rendered as perspective projections based on the relative positions between the models. The projection geometry of the software was validated by developing an artificial CT data set containing high attenuation points as objects to be imaged. The accuracy in projection geometry was evaluated in a systematic way. The distances between two dots, representing the projected test points in the simulated radiographic images, were measured. They were compared with theoretical calculations of the corresponding distances using traditional mathematical tools.
  
  
  RESULTS
  The difference between the simulated and calculated projected distances never exceeded 0.5 mm. The error in simulated projected distances was in most cases within 1%. No systematic errors were revealed.
  
  
  CONCLUSIONS
  The software, developed for personal computers, can produce simulated X-ray images with high geometric accuracy based on perspective projections through a CT data set. The software can be used for simulation of radiographic examinations.
authors.affiliation: Oral and Maxillofacial Radiology, Department of Odontology, Ume University, Ume, Sweden. tore.nilsson@odont.umu.se
authors.forename: T
authors.initials: T
authors.lastname: Nilsson
authors.forename: J
authors.initials: J
authors.lastname: Ahlqvist
authors.forename: M
authors.initials: M
authors.lastname: Johansson
authors.forename: A
authors.initials: A
authors.lastname: Isberg
mesh_terms: D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008838:Microcomputers; D011861:Radiography, Dental; D012886:Skull / Q000000981:diagnostic imaging; D012985:Software Design; D012986:Software Validation; D014057:Tomography, X-Ray Computed; D014584:User-Computer Interface