title: In vitro calibration and validation of a digital subtraction radiography system using scanned images.
abstract: OBJECTIVE
  To calibrate and validate a digital subtraction radiography system using scanned images for quantification of alveolar bone changes by means of computer-assisted densitometric image analysis (CADIA) in vitro.
  
  
  METHODS
  Noise levels were determined using 10 standardized periapical radiographs of the same lower molar region in a human dry skull. For validation of the system, radiographs were taken before and after bovine bone particles in measures with increments of 2 mg weighing from 2 to 20 mg were added into each socket of three dry skulls. Radiographs were developed and scanned into a computer with a flatbed scanner. After digitization, the images were subjected to alignment, normalization and subtraction. Appropriate regions of interest (ROIs) were selected and their CADIA values were calculated for the determination of noise levels, and correlations between the CADIA values and the actual bone mass were performed.
  
  
  RESULTS
  When the threshold value was 7, the percentage of pixels deviating from the set threshold value was small (0-11.3%). There were statistically significant correlations between the actual bone mass and the CADIA value for anterior sockets (p<0.001, r2=0.89) and posterior sockets (p<0.001, r2=0.9). For pooled data of both anterior and posterior sockets, the correlation was also statistically significant (p<0.001, r2=0.88).
  
  
  CONCLUSIONS
  A high and statistically significant correlation between the actual bone mass and CADIA value was obtained, which suggests that the system could be suitable for the detection of small alveolar bone changes.
authors.affiliation: Faculty of Dentistry, The University of Hong Kong, Hong Kong.
authors.forename: B M S
authors.initials: BM
authors.lastname: Woo
authors.forename: K-Y
authors.initials: KY
authors.lastname: Zee
authors.forename: F H Y
authors.initials: FH
authors.lastname: Chan
authors.forename: E F
authors.initials: EF
authors.lastname: Corbet
mesh_terms: D015502:Absorptiometry, Photon; D016301:Alveolar Bone Loss / Q000000981:diagnostic imaging*; D000818:Animals; D016477:Artifacts; D002138:Calibration; D002417:Cattle; D006801:Humans; D016018:Least-Squares Analysis; D011857:Radiographic Image Interpretation, Computer-Assisted; D019252:Radiography, Dental, Digital; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D020390:Tooth Socket / Q000000981:diagnostic imaging*