title: The design of an fast Fourier filter for enhancing diagnostically relevant structures - endodontic files.
abstract: BACKGROUND
  The endodontic working length is commonly determined by electronic apex locators and intraoral periapical radiographs. No algorithms for the automatic detection of endodontic files in dental radiographs have been described in the recent literature.
  
  
  METHODS
  Teeth from the mandibles of pig cadavers were accessed, and digital radiographs of these specimens were obtained using an optical bench. The specimens were then recorded in identical positions and settings after the insertion of endodontic files of known sizes (ISO sizes 10-15). The frequency bands generated by the endodontic files were determined using fast Fourier transforms (FFTs) to convert the resulting images into frequency spectra. The detected frequencies were used to design a pre-segmentation filter, which was programmed using Delphi XE RAD Studio software (Embarcadero Technologies, San Francisco, USA) and tested on 20 radiographs. For performance evaluation purposes, the gauged lengths (measured with a caliper) of visible endodontic files were measured in the native and filtered images.
  
  
  RESULTS
  The software was able to segment the endodontic files in both the samples and similar dental radiographs. We observed median length differences of 0.52 mm (SD: 2.76 mm) and 0.46 mm (SD: 2.33 mm) in the native and post-segmentation images, respectively. Pearson's correlation test revealed a significant correlation of 0.915 between the true length and the measured length in the native images; the corresponding correlation for the filtered images was 0.97 (p=0.0001).
  
  
  CONCLUSIONS
  The algorithm can be used to automatically detect and measure the lengths of endodontic files in digital dental radiographs.
authors.affiliation: Department of oral Surgery, University Medical Center Mainz, Augustusplatz 2, 55131 Mainz, Germany.
authors.forename: Dan
authors.initials: D
authors.lastname: Bruellmann
authors.affiliation: Department of oral Surgery, University Medical Center Mainz, Augustusplatz 2, 55131 Mainz, Germany.
authors.forename: Steven
authors.initials: S
authors.lastname: Sander
authors.affiliation: IMBEI, University Medical Center Mainz, Germany.
authors.forename: Irene
authors.initials: I
authors.lastname: Schmidtmann
mesh_terms: D000818:Animals; D004708:Endodontics; D005583:Fourier Analysis; D013552:Swine
keywords: Detection; Digital radiography; Endodontic files; Needles