• Progress in Medical Physics
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• v.19 no.1
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• pp.63-72
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• 2008

With recent advancement of the medical imaging systems and picture archiving and communication system (PACS), installation of digital radiography has been accelerated over past few years. Moreover, Computed Radiography (CR) which was well established for the foundation of digital x-ray imaging systems at low cost was widely used for clinical applications. This study analyzes imaging characteristics for two systems with different pixel sizes through the Modulation Transfer Function (MTF), Noise Power Spectrum (NPS) and Detective Quantum Efficiency (DQE). In addition, influence of radiation dose to the imaging characteristics was also measured by quantitative assessment. A standard beam quality RQA5 based on an international electro-technical commission (IEC) standard was used to perform the x-ray imaging studies. For the results, the spatial resolution based on MTF at 10% for Agfa CR system with I.P size of $8{\times}10$ inches and $14{\times}17$ inches was measured as 3.9 cycles/mm and 2.8 cycles/mm, respectively. The spatial resolution based on MTF at 10% for Fuji CR system with I.P size of $8{\times}10$ inches and $14{\times}17$ inches was measured as 3.4 cycles/mm and 3.2 cycles/mm, respectively. There was difference in the spatial resolution for $14{\times}17$ inches, although radiation dose does not effect to the MTF. The NPS of the Agfa CR system shows similar results for different pixel size between $100{\mu}m$ for $8{\times}10$ inch I.P and $150{\mu}m$ for $14{\times}17$ inch I.P. For both systems, the results show better NPS for increased radiation dose due to increasing number of photons. DQE of the Agfa CR system for $8{\times}10$ inch I.P and $14{\times}17$ inch I.P resulted in 11% and 8.8% at 1.5 cycles/mm, respectively. Both systems show that the higher level of radiation dose would lead to the worse DQE efficiency. Measuring DQE for multiple factors of imaging characteristics plays very important role in determining efficiency of equipment and reducing radiation dose for the patients. In conclusion, the results of this study could be used as a baseline to optimize imaging systems and their imaging characteristics by measuring MTF, NPS, and DQE for different level of radiation dose.

• Journal of the Korean Society of Radiology
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• v.13 no.4
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• pp.589-596
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• 2019

X-rays used for diagnosis have a continuous energy distribution. However, photons with low energy not only reduce image contrast, but also contribute to the patient's radiation exposure. Therefore, clinics currently use filters made of aluminum. Such filters are advantageous because they can reduce the exposure of the patient to radiation. However, they may have negative effects on imaging quality, as they lead to increases in the scattered dose. In this study, we investigated the effects of the scattered dose generated by an aluminum filter on medical image quality. We used the relative standard deviation and the scatter degradation factor as evaluation indices, as they can be used to quantitatively express the decrease in the degree of contrast in imaging. We verified that the scattered dose generated by the increase in the thickness of the aluminum filter causes degradation of the quality of medical images.

• The Journal of the Korean dental association
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• v.50 no.4
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• pp.180-188
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• 2012

Cone beam computed tomography(CBCT) machines recently developed in Korea, being designed for imaging hard tissues of the oral and maxillofacial region. I reported a brief overview of CBCT system, in comparison with coventional computed tomography(CT) system. CBCT provides high resolution, simpler image acquisition, lower dose and cost alternative to conventional CT, promising to revolutionize the practice of oral and maxillofacial radiology.

• Journal of radiological science and technology
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• v.40 no.1
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• pp.71-78
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• 2017

Scattered radiation is inherent phenomenon of x-ray, which occurs to the subject (or patient). Therefore it cannot be avoidable but also interacts as serious noise factor because the only meaningful information on x-ray radiography is primary x-ray photons. The purpose of this study was to quantify scattered radiation for various shooting parameters and to verify the effect of anti-scatter grid. We employed beam stopper method to characterize scatter to primary ratio. To evaluate effect on the projection images calculated contrast to noise ratio of given shooting parameters. From the experiments, we identified the scattered radiation increases in thicker patient and smaller air gap. Moreover, scattered radiation degraded contrast to noise ratio of the projection images. We find out that the anti-scatter grid rejected scattered radiation effectively, however there were not fewer than 100% of scatter to primary ratio in some shooting parameters. The results demonstrate that the scattered radiation was serious problem of medical x-ray system, we confirmed that the scattered radiation was not considerable factor of dig ital radiog raphy.

• Imaging Science in Dentistry
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• v.42 no.4
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• pp.237-242
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• 2012

Purpose: The objectives of this study were to survey the radiographic exposure parameters, to measure the patient doses for intraoral dental radiography nationwide, and thus to establish the diagnostic reference levels (DRLs) in intraoral dental X-ray examination in Korea. Materials and Methods: One hundred two intraoral dental radiographic machines from all regions of South Korea were selected for this study. Radiographic exposure parameters, size of hospital, type of image receptor system, installation duration of machine, and type of dental X-ray machine were documented. Patient entrance doses (PED) and dose-area products (DAP) were measured three times at the end of the exit cone of the X-ray unit with a DAP meter (DIAMENTOR M4-KDK, PTW, Freiburg, Germany) for adult mandibular molar intraoral dental radiography, and corrections were made for room temperature and pressure. Measured PED and DAP were averaged and compared according to the size of hospital, type of image receptor system, installation duration, and type of dental X-ray machine. Results: The mean exposure parameters were 62.6 kVp, 7.9 mA, and 0.5 second for adult mandibular molar intraoral dental radiography. The mean patient dose was 2.11 mGy (PED) and 59.4 $mGycm^2$ (DAP) and the third quartile one 3.07 mGy (PED) and 87.4 $mGycm^2$ (DAP). Doses at university dental hospitals were lower than those at dental clinics (p<0.05). Doses of digital radiography (DR) type were lower than those of film-based type (p<0.05). Conclusion: We recommend 3.1 mGy (PED), 87.4 $mGycm^2$ (DAP) as the DRLs in adult mandibular molar intraoral dental radiography in Korea.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.1
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• pp.19-28
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• 1996

This study has investigated the optimization of NDT method and the minimum detectable defect size for complex structures such as the solid propellant rocket motor using real time X-ray imaging system. Test specimens were made of steel plates with various defect size, and installed with proper thickness for which solid propellant, rubber, and case converted to the steel equivalent thickness according to the radiographic equivalent theory. As the results, this examination obtained optimum magnification and X-ray energy, dose rate according to steel equivalent thickness, also, obtained the relationship between minimum detectable defect size and the ratio(defect depot/object thickness). Thus, this simulated test is the preliminary procedure before performing NDT for real objects, and is possibly applied for NDT of other complex structures.

• Korean Journal of Digital Imaging in Medicine
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• v.13 no.3
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• pp.139-144
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• 2011

The purpose of this report is recommending a standard indicator which reflects the radiation exposure that is incident on a detector after every exposure event and that reflects the noise levels present in the image data. The experiment was performed with mobile digital X-ray unit and used a acrylic phantom for exposure index measurement. Exposure modality was kVp, mAs, SID. After every exposure, make a data sheet for characteristic curve of detector response. The equipment performed Mobile digital X-ray unit provide the user with values ralated to the incident exposure(air kerma)to the digital detector. They are showed as a logarithmic function shaped. As a result, DEI means a relative measure of exposure to the detector, as compared to the expected exposure for a particular anatomical view. Radiographic technique is the combination of factors used to exposure an anatomical part to produce a high quality radiography and technique charts used most commonly by radiographers to produce consistently exposure level which patient dose can be kept acceptably low.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.417-426
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• 2006

A Digital X-ray imaging system using Compton backscattering has been developed to obtain a cross-sectional profile and mass loss of corroded lap-splices of aging aircraft from density variation. A slit-type camera was designed to focus on a small scattering volume inside the material, from which the backscattered photons are collected by a collimated scintillator detector for interpretation of material characteristics. The cross section of the lap-joint is scanned by moving the scattering volume through the thickness direction of the specimen. The mass loss of each layer has been estimated from a Compton backscatter A-scan to obtain the thickness of each layer including the aluminum sheet, the corrosion layer and the sealant. Quantitative information such as location and width of planar corrosion in the lap splices of fuselages is obtained by deconvolution using a nonlinear least-square error minimization method(BFGS method): A simple reconstruction model is also introduced to overcome distortion of the Compton backscatter data due to attenuation effects attributed to beam hardening and quantum noise.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.61.2-61.2
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• 2018

ZwCL 1447.2+2619 is a merging galaxy cluster at z=0.37 with clear substructures in X-ray emission and galaxy distribution. In addition, the system possesses distinct radio relics. In order to constrain the merger scenario, it is necessary to measure both the distribution and mass of the cluster dark matter. We perform weak lensing analysis of ZwCL 1447.2+2619 using Subaru imaging data. We detect clear lensing signal from the cluster after carefully addressing instrumental systematics. In this poster, we present our preliminary results on our mass reconstruction and discuss the comparison with X-ray and radio results.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1475-1478
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• 2008

We have investigated the blood sucking phenomena of a female mosquito. The main objective of this study is to understand the mosquito's blood sucking mechanism and eventually to develop a bio-mimic technology that can be used to resolve the problem encountered in the transport of infinitesimal biological fluids in various bio-chips and microchips. At first, the consecutive velocity fields of blood-sucking flow in a proboscis were measured using a micro-particle image velocimetry (PIV) system employed with a high-speed camera. The velocity signals of the blood-sucking flow in the proboscis represent a periodic pulsatile flow pattern and spectral analysis on the velocity waveform shows a clear peak at 6.1 Hz.