title: A method to calculate angular disparities between object and receptor in "paralleling technique".
abstract: OBJECTIVE
  To develop an image analysis method for calculation of angular disparities between an object, temporarily equipped with a reference system, and a radiographic receptor.
  
  
  METHODS
  A mathematical method based on a reference system containing two metallic spheres is developed, allowing calculation of inclination between the inter-spherical axis and the digital image receptor using image features. Experimental evaluation was done in standardized projection geometry for two sphere sizes at four randomly chosen inclinations per size, with each radiograph assessed three times. Truth was assessed threefold from photographs obtained at each inclination.
  
  
  RESULTS
  Mean standard deviation between single assessments was 2.6 degrees. Significant differences (P Maloney/Rastogy=0.00) were found between absolute values of truth and calculated values (mean: -0.9 degrees; range: -6.0 degrees; 3.6 degrees), indicating a significant lack of accuracy.
  
  
  CONCLUSIONS
  Although so far not sufficiently accurate, the method yields information relevant for correction of distortion in intra-oral radiology.
authors.affiliation: Department of Oral Surgery, Dental School, Johannes Gutenberg University, Augustusplatz 2, 55131 Mainz, Germany. rschulze@mail.uni-mainz.de
authors.forename: R K W
authors.initials: RK
authors.lastname: Schulze
authors.forename: B
authors.initials: B
authors.lastname: d'Hoedt
mesh_terms: D000465:Algorithms; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000706:statistics & numerical data*; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D010781:Photography; D011858:Radiographic Magnification / Q000706:statistics & numerical data; D019252:Radiography, Dental, Digital / Q000706:statistics & numerical data*