Korean J Oral Maxillofac Radiol.
2002 Jun;32(2):75-79.
Effect of exposure time and image resolution on fractal dimension
- Affiliations
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- 1Department of Oral and Maxillofacial Radiology and Dental Research Institute, College of Dentistry, Seoul National University, Korea. raychoi@snu.ac.kr
- 2Department of Oral Anatomy and Dental Research Institute, College of Dentistry, Seoul National University, Korea.
- 3Department of Oral and Maxillofacial Radiology, Dental Research Institute, and BK21, College of Dentistry, Seoul National University, Korea.
- 4Division of Information and Communication Engineering, Hallym University, Korea.
Abstract
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PURPOSE: To evaluate the effect of exposure time and image resolution on fractal dimension calculations for determining the optimal range of these two variances.
MATERIALS AND METHODS
Thirty-one radiographs of the mandibular angle area of sixteen human dry mandibles were taken at different exposure times (0.01, 0.08, 0.16, 0.25, 0.40, 0.64, and 0.80 s). Each radiograph was digitized at 1200 dpi, 8 bit, 256 gray level using a film scanner. We selected an Region of Interest (ROI) that corresponded to the same region as in each radiograph, but the resolution of ROI was degraded to 1000, 800, 600, 500, 400, 300, 200, and 100 dpi. The fractal dimension was calculated by using the tile-counting method for each image, and the calculated values were then compared statistically.
RESULTS
As the exposure time and the image resolution increased, the mean value of the fractal dimension decreased, except the case where exposure time was set at 0.01 seconds (alpha = 0.05). The exposure time and image resolution affected the fractal dimension by interaction (p<0.001). When the exposure time was set to either 0.64 seconds or 0.80 seconds, the resulting fractal dimensions were lower, irrespective of image resolution, than at shorter exposure times (alpha = 0.05). The optimal range for exposure time and resolution was determined to be 0.08-0.40 seconds and from 400-1000 dpi, respectively.
CONCLUSION
Adequate exposure time and image resolution is essential for acquiring the fractal dimension using tile-counting method for evaluation of the mandible.
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