THE EFFECT OF IMAGE VARIATIONS ON FRACTAL DIMENSION CALCULATIONS

Objectives. We used digitized dental radiographs of alveolar bone to t est the hypothesis that the fractal dimension, as calculated with the program ''lmageFractal'' was independent of variations in x-ray exposu re, beam alignment, and region of interest placement. Study design. Th e radiographic data set consisted of 72 radiographs digitized with 200 mu m pixels. Radiographs were obtained with the use of three time set tings and two alignments. Rectangular regions of interest were placed on each digital image over the interdental bone between the mandibular first and second molars on six hemimandibles. Each of six hemimandibl es had identical copies of a unique region of interest placed on every image in its series. New regions were made 3 months later. A fractal dimension was computed from each region of interest with the caliper m ethod included in ImageFractal, a public domain program available thro ugh National institutes of Health. The resulting fractal dimensions we re evaluated with two repeated measures analysis of variance. Results. No significant differences were found between the fractal dimensions calculated for baseline images and those from overexposed and underexp osed images, from images with 4 to 6 degrees of alignment variations, or from repeat regions of interest. Conclusion. The results support th e hypothesis that fractal dimensions derived from digitized dental rad iographs are not affected by variations in exposure or small variation s in alignment and imply an absolute region of interest placement may not be necessary. However, caution should be used with the use of the fractal dimension to discriminate among alveolar bone variations until further research is performed.