ABSTRACT
Objective: cone beam computed tomography [CBCT] is applied for the imaging of the maxillofacial and dental structures, particularly for surgical treatments and dental implants. The aim of this study was to assess the effect of slice thickness on the accuracy of CBCT linear measurements
Methods: in this diagnostic accuracy study, forty-two titanium pins with the same dimensions were inserted into seven dry sheep mandibles. The length of the pins before the insertion was carefully measured by a digital caliper, [0.01mm accuracy]. Imaging of the mandible performed using CBCT New Tom VGi. After image reconstruction by NNT Viewer, linear measurements were made on cross-sectional slices [thicknesses of 0.125, 0.5, 1 and 2mm] by three radiologists. The accuracy of measurements assessed using descriptive indices and compared between different slice thicknesses by repeated measures ANOVA
Results: repeated measures ANOVA showed a significant difference between different slice thicknesses [P=0.024]. According to the least significant difference [LSD] test, the difference in absolute errors was significant in all thicknesses [P=0.024]. Measurements at 0.125 mm thickness were significantly different from others, with a higher error rate [mean absolute error=0.17]. Measurements at 0.5mm thickness showed a significant difference with those at 0.125 and 2mm [mean absolute error=0.15]. Measurements at 2mm thickness were significantly different from those at 0.125 mm thickness [mean absolute error=0.13].The average error rate was lower in 2mm thickness and the measurements were more accurate
Conclusion: a statistically significant difference was seam between CBCT measurements and actual sizes in different slice thicknesses. The differences were below 1mm, and clinically acceptable
ABSTRACT
Objective: When none of digital systems and scanners is accessible and it is essential to have digitized images of conventional radiographs, digital cameras can be used. The Aim of this study was to investigate whether digital images obtained by different resolutions of a digital camera are matched to the original radiographs in evaluation of caries
Methods: In this diagnostic accuracy in vitro study the conventional radiographs of168 proximal surfaces of 84 teeth were produced, Then they were digitized with digital camera in three different resolutions; high [2048x1536], medium [1600x1200] and low resolution [480x460]. Images were stored in Photoshop7.0 software, and were evaluated by5 observers to show the presence and depth of the caries. Cronbach's [alpha] calculated inter-observers agreement and in order to calculate the agreement with original conventional radiographs Kappa index was used
Results: In assessing the presence of caries, the agreement between low, medium and high resolutions with original radiographs were 0.286, 0.235 and 0 respectively. Also, assessing the depth of the caries agreement was reported0.21, 0.338 and 0.412 respectively. In most instances, there was a fair agreement between the different resolutions and original radiographs. The highest interobserver's agreement was reported in diagnosis of the presence of the caries with using high resolution [[alpha]=0.837] and the lowest inter-observer's agreement was reported in diagnosis of the depth of the caries with medium resolution [[alpha]=0.762].There was no significant difference reported in observations of different resolutions and original images
Conclusion: Using of high-resolution cameras did not show a significant difference with medium and low resolutions in caries evaluations. Therefore, considering the increase in the file size and difficulties in cameras selection, using of high-resolution digital cameras is not necessary in order to increase the diagnostic accuracy of digitized images