ABSTRACT
OBJECTIVE@#To propose a sensitivity test method for geometric correction position deviation of cone-beam CT systems.@*METHODS@#We proposed the definition of center deviation and its derivation. We analyzed the influence of the variation of the three-dimensional spatial center of the steel ball point, the projection center and the size of the steel ball point on the deviation of geometric parameters and the reconstructed image results by calculating the geometric correction parameters based on the Noo analytical method using the FDK reconstruction algorithm for image reconstruction.@*RESULTS@#The radius of the steel ball point was within 3 mm. The deviation of the center of the calibration parameter was within the order of magnitude and negligible. A 10% Gaussian perturbation of a single pixel in the 3D spatial coordinates of the steel ball point produced a deviation of about 3 pixel sizes, while the same Gaussian perturbation of the 2D projection coordinates of the steel ball point produced a deviation of about 2 pixel sizes.@*CONCLUSION@#The geometric correction is more sensitive to the deviation generated by the three-dimensional spatial coordinates of the steel ball point with limited sensitivity to the deviation generated by the two-dimensional projection coordinates of the steel ball point. The deviation sensitivity of a small diameter steel ball point can be ignored.
Subject(s)
Algorithms , Calibration , Cone-Beam Computed Tomography , SteelABSTRACT
30 preadolescent children with anterior crossbite were selected for the present study. Among them 15 were male and 15 children were female. Their age ranged from 8 to 12 years. The mean age was 10. 8 years. Their perioral forces were measured in the areas as following: the labial and lingual sides of mandibular and maxillar central incisors, the first premolars and molars of both sides. After analysis of the results, some conclusions were drawn as the following, the distribution of the perioral force of bilateral arch was symmetric, and there were no significant differences between genders. The values of the perioral force in the premolar and molar area were the largest. When the children were in their nature head position, the perioral force values of labial side were larger than those on the lingual side. On the lingual side of mandibular incisors negative values were found. The perioral force correlated with malocclusion. The position of the teeth decides the value of the perioral force. It has been well concluded that the forces exerted on the teeth were not the only factor that influenced teeth position. There are also other factors influencing the teeth poison. This needs further study.
