title: The effect of varying the region of interest on calculations of fractal index.
abstract: OBJECTIVE
  To compare the effect of using regions of interest (ROIs) of different size and shape on the fractal index of alveolar bone.
  
  
  METHODS
  Two sets of clinical posterior bitewing radiographs were used to calculate the fractal index (S). Two comparisons were made. First, S was calculated from large interdental ROIs that included small amounts of root structure and compared with S from small ROIs that included no root structures. Then S was calculated from large interdental ROIs (similar to those used for the first set) and compared with S calculated from ROIs that included nearly all of the mandibular alveolar bone (and adjacent root) present on the bitewing.
  
  
  RESULTS
  For the first comparison, paired t-tests showed that fractal indices calculated with the large ROIs were significantly different from the respective indices calculated from the small ROIs (P < 0.001). For the second comparison, the fractal indices calculated from the large quadrant ROIs were not significantly different from those calculated from the large ROIs (P = 0.120).
  
  
  CONCLUSIONS
  ROI size and shape may affect the results of fractal analysis of alveolar bone.
authors.affiliation: Oral Diagnosis and Patient Services, School of Dentistry, Medical College of Georgia, Augusta 30912-1241, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Shrout
authors.forename: C F
authors.initials: CF
authors.lastname: Hildebolt
authors.forename: B J
authors.initials: BJ
authors.lastname: Potter
mesh_terms: D000539:Alveolar Process / Q000000981:diagnostic imaging; D005260:Female; D017709:Fractals; D006801:Humans; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D016300:Radiography, Bitewing / Q000379:methods; D019252:Radiography, Dental, Digital / Q000379:methods*