title: Software for automated application of a reference-based method for a posteriori determination of the effective radiographic imaging geometry.
abstract: OBJECTIVE
  Presentation and validation of software developed for automated and accurate application of a reference-based algorithm (reference sphere method: RSM) inferring the effective imaging geometry from quantitative radiographic image analysis.
  
  
  METHODS
  The software uses modern pattern recognition and computer vision algorithms adapted for the particular application of automated detection of the reference sphere shadows (ellipses) with subpixel accuracy. It applies the RSM algorithm to the shadows detected, thereby providing three-dimensional Cartesian coordinates of the spheres. If the three sphere centres do not lie on one line, they uniquely determine the imaging geometry. Accuracy of the computed coordinates is investigated in a set of 28 charge-coupled device (CCD)-based radiographs of two human mandible segments produced on an optical bench. Each specimen contained three reference spheres (two different radii r1=1.5 mm, r2=2.5 mm). True sphere coordinates were assessed with a manually operated calliper. Software accuracy was investigated for a weighted and unweighted algebraic ellipse-fitting algorithm.
  
  
  RESULTS
  The critical depth- (z-) coordinates revealed mean absolute errors ranging between 1.1+/-0.7 mm (unweighted version; r=2.5 mm) and 1.4+/-1.4 mm (weighted version, r=2.5 mm), corresponding to mean relative errors between 5% and 6%. Outliers resulted from complete circular dense structure superimposition and one obviously deformed reference sphere.
  
  
  CONCLUSIONS
  The software provides information fundamentally important for the image formation and geometric image registration, which is a crucial step for three-dimensional reconstruction from > or =2 two-dimensional views.
authors.affiliation: Department of Oral Surgery, Johannes Gutenberg-University, Mainz, Germany. rschulze@mail.uni-mainz.de
authors.forename: R K W
authors.initials: RK
authors.lastname: Schulze
authors.forename: O
authors.initials: O
authors.lastname: Weinheimer
authors.forename: D D
authors.initials: DD
authors.lastname: Brüllmann
authors.forename: F
authors.initials: F
authors.lastname: Röder
authors.forename: B
authors.initials: B
authors.lastname: d'Hoedt
authors.forename: E
authors.initials: E
authors.lastname: Schoemer
mesh_terms: D000465:Algorithms; D001185:Artificial Intelligence; D002138:Calibration; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D021621:Imaging, Three-Dimensional / Q000379:methods; D008334:Mandible / Q000000981:diagnostic imaging; D010363:Pattern Recognition, Automated; D019252:Radiography, Dental, Digital / Q000379:methods*; D012984:Software; D012985:Software Design; D012986:Software Validation