• Imaging Science in Dentistry
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• v.44 no.4
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• pp.279-285
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• 2014

Purpose: To assess the influence of anatomic location on the relationship between computed tomography (CT) number and X-ray attenuation in limited and medium field-of-view (FOV) scans. Materials and Methods: Tubes containing solutions with different concentrations of $K_2HPO_4$ were placed in the tooth sockets of a human head phantom. Cone-beam computed tomography (CBCT) scans were acquired, and CT numbers of the $K_2HPO_4$ solutions were measured. The relationship between CT number and $K_2HPO_4$ concentration was examined by linear regression analyses. Then, the variation in CT number according to anatomic location was examined. Results: The relationship between $K_2HPO_4$ concentration and CT number was strongly linear. The slopes of the linear regressions for the limited FOVs were almost 2-fold lower than those for the medium FOVs. The absolute CT number differed between imaging protocols and anatomic locations. Conclusion: There is a strong linear relationship between X-ray attenuation and CT number. The specific imaging protocol and anatomic location of the object strongly influence this relationship.

• Nuclear Engineering and Technology
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• v.44 no.1
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• pp.61-70
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• 2012

In this study, a simple post-reconstruction dual-energy computed tomography (CT) method is proposed. A dual-energy CT algorithm for monochromatic x-rays was adopted and applied to the dual-energy CT of polychromatic x-rays by assigning a representative mono-energy. The accuracy of algorithm implementation was tested with mathematical phantoms. To test the sensitivity of this algorithm to the inaccuracy of representative energy value in energy values, a simulation study was performed with mathematical phantom. To represent a polychromatic x-ray energy spectrum with a single-energy, mean energy and equivalent energy were used, and the results were compared. The feasibility of the proposed method was experimentally tested with two different micro-CTs and a test phantom made of polymethyl methacrylate (PMMA), water, and graphite. The dual-energy calculations were carried out with CT images of all possible energy pairs among 40, 50, 60, 70, and 80 kVp. The effective atomic number and the electron density values obtained from the proposed method were compared with theoretical values. The results showed that, except the errors in the effective atomic number of graphite, most of the errors were less than 10 % for both CT scanners, and for the combination of 60 kVp and 70 kVp, errors less than 6.0 % could be achieved with a Polaris 90 CT. The proposed method shows simplicity of calibration, demonstrating its practicality and feasibility for use with a general polychromatic CT.

• Imaging Science in Dentistry
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• v.35 no.4
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• pp.231-234
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• 2005

Coronoid impingement can cause limitation of mouth opening. In many cases, it appears to be related to the coronoid hyperplasia. We present a case of mouth opening limitation caused by coronoid impingement on the posterior surface of the zygomatic bone without coronoid hyperplasia. The bony changes in coronoid and zygoma including surface irregularity and discontinuity of the cortex and sclerotic change of inner medullary space were noted on computed tomography (CT) scans in different level of axial planes. Through another CT scans in open mouth position could demonstrate that those bony changes were caused by the contact of both surfaces against each other. In case coronoid impingement is suspected of the many possible causes, the open mouth CT scans will be needed to reveal the direct impingement of coronoid on zygoma even without coronoid hyperplasia.

• Imaging Science in Dentistry
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• v.35 no.3
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• pp.167-173
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• 2005

Purpose : To investigate the relationship between three-dimensional (3D) bone imaging parameters and trabecular strength in the mandible. Materials and Methods : Bone specimens were obtained from the mandibles of five male pigs weighing around 110 kg each. Of those, 43 samples were selected for 3D analysis and measured by micro-computed tomography. The five morphometric parameters were trabecular thickness (Tb.Th), bone specific surface (BS/BV), percent bone volume (BV/TV), structure model index (SMI) and degree of anisotropy (DA). Through destructive mechanical testing, strength parameters were obtained. Results : BV/TV, SMI, BS/BV, and Tb.Th showed significant correlations with strength parameters. DA did not show any correlation with the other parameters. In multiple linear regression analysis, BV/TV alone explained $43\%$ of the variance in Young's modulus. By stepwise inclusion of SMI, the variance in the Young's modulus was better explained up to $52\%$. Conclusions : Predicting trabecular strength in the mandible through architectural analysis would be possible. Further study is needed to establish the tendency and variety of trabecular architecture and strength according to the locations within the mandible.

• Journal of the korean academy of Pediatric Dentistry
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• v.49 no.1
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• pp.57-64
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• 2022

Additional dentition images are needed because the dentitions are distorted in cone-beam computed tomography (CBCT) due to streak artifacts and non-uniformity of the x-ray beam. The purpose of this study is to evaluate the feasibility of improving the dentition image of CBCT scan with intraoral scanner instead of plaster models. Maxilla images from plaster models, two intraoral scanners, and CBCT of 20 patients aged 12 to 18 were used in this study. With one of the intraoral scanners, the full arch was scanned by three segments and combined into a complete full arch. Virtual skull-dentition hybrid images from intraoral scanners were superimposed with the images from plaster models to evaluate the coordinate value difference and distance at reference points. The results showed that the coordinate value difference and distance were smallest with segmented intraoral scan, which showed only 2 ㎛ distance. Intraoral scan may provide good dentition images for virtual skull-dentition images.

• Korean Journal of Veterinary Research
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• v.54 no.3
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• pp.151-157
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• 2014

A nationwide survey on radiation safety management in Korean animal hospitals was conducted. By 2013, 53 radiation generators were registered as veterinary medical devices (41 X-ray generators and 12 computed tomography scanners). Additionally there were six approved laboratories for radiation equipment and protection facility, and five approved laboratories for radiation exposure of employees, respectively. By March 2013, 2,030 out of 3,829 animal hospitals operated radiation-generating devices. Among these devices, 389 (19.2%) out of 2,030 were not labeled with the model name and 746 (36.7%) were not labeled with production dates. Thus, most veterinary X-ray generators were outdated (42.6%) and needed replacements. When periodic inspections of 2,018 animal hospitals were performed after revision of the Veterinarians Act in 2011, the hospitals were found to be equipped with appropriate radiation generators and protection facilities. Among 2,545 employees exposed to radiation at the hospitals, 93.9% were veterinarians, 4.3% were animal nurse technicians, and 18% held other positions. Among 169 employees supervised by administrators, none of those had a weekly maximum operating load that exceeded $10mA{\cdot}min$. This study suggests that the radiation safety management system of animal hospitals was general good.

• Journal of Korean Neurosurgical Society
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• v.59 no.5
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• pp.466-470
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• 2016

Objective : To determine imaging features that may separate adamantinomatous and papillary variants of craniopharyngiomas given that tumors with adamantinomatous signature features are associated with higher recurrence rates, morbidity, and mortality. We specifically reviewed calcification on CT, T1 bright signal intensity, and cystic change on T2 weighted images for differentiating these two types. Methods : We retrospectively reviewed the MRI and CT studies in 38 consecutive patients with pathologically proven craniopharyngiomas between January 2004 and February 2014 for the presence of calcification on CT scans, bright signal intensity on T1 weighted images, and cystic change on T2 weighted images. Results : Of the 38 craniopharyngiomas, 30 were adamantinomatous type and 8 were papillary type. On CT scans, calcification was present in 25 of 38 tumors. All calcified tumors were adamantinomatous type. Twenty four of 38 tumors had bright signal intensity on T1 weighted images. Of these 24 tumors, 22 (91.7%) were adamantinomatous and 2 were papillary type. Cystic change on T2 weighted images was noted in 37 of 38 tumors; only 1 tumor with papillary type did not show cystic change. Conclusion : T1 bright signal intensity and calcification on CT scans uniformly favor the adamantinomatous type over papillary type of craniopharyngioma in children. However, these findings are more variable in adults where calcification and T1 bright signal intensity occur in 70.6% and 58.8% respectively of adult adamantinomatous types of craniopharyngiomas.