디지탈영상에서 골판톰의 프랙탈분석
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- A Fractal Analysis of Bone Phantoms from Digital Images
Chang-Yul Lee D.D.S.,M.S.D.
Director Jae-Duk Kim Ph.D.
Dept. of Dentistry, Graduate School,
This study was performed to analyse the effect of exposure time, ROI size and one impact factor during the image processing procedure on estimates of fractal dimension; and to analyse the correlated relationship between the fractal dimension and the bone density(Cu-Eq value). The two resin blocks containing the cylindric bone phantoms of 6 large and 5 small diameter having different bone densities respectively and human dry mandible segment with copper step wedge were radiographed at 1.0 and 1.2 sec esposure(70kVp, 7mA) using one occlusal film and digitized with a flat-bed scanner. Eleven rectangular ROIs from 11 cylindric bone phantoms and 4 rectangular ROIs from cortical, middle, periodontal regions, and socket of bone were selected. Gaussian blurred Image was subtracted from original image of each ROI and multiplied respectively by 1, 0.8, and 0.5, and then the image was made binary, eroded and dilated once, and skeletonized. The fractal dimension was calculated by means of a box counting method in the software ImageJ.
The obtained results were as follows:
1. With the change in the number of the modifying factor during the image subtracting procedure, the cases that fractal dimension failed to show the consistency during subsequently lowered bone density were appeared.
2. The fractal dimension was decreased gradually with continued bone density decrease showing strong correlations(bone phantom; r>0.87, bone; r>0.68) under 70kVp 1.0sec M=0.8.
3.Fractal dimensions showed the significant differerence(p<0.05) between under two different exposure times on the same small ROI of bone phantom.
4.Fractal dimensions between two different sizes of ROI on bone phantom showed the significant differerence(p<0.05) under 1.2sec exposure, but did not (p>0.05) under 1.0 sec exposure.
In conclusion, exposure time, ROI size, and modifying factor during subtracting could be impacting factors on the results of fractal dimension. Fractal analysis with thoroughly evaluated method considering the various impacting factors on the results could be useful in assessing the bone density in dental radiography.
Keywords: radiography, dental; fractals; bone; image processing
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