• Imaging Science in Dentistry
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• v.35 no.2
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• pp.87-90
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• 2005

Purpose : The purpose of this study was to investigate variability of doses with same exposure parameters and evaluate radiographic density according to the variability of doses. Materials and methods Twenty-eight MAX-GLS (Shinhung Co, Seoul, Korea), twenty-one D-60-5 (DongSeo Med, Seoul, Korea), and eleven REX-601 (Yoshida Dental MFG, Tokyo, Japan) dental x-ray machines were selected for this study Surface doses were measured under selected combinations of tube voltage, tube current, exposure time, and constant distance 42 cm from the focal spot to the surface of the Multi-O-meter (Unfors Instruments, Billdal, Sweden). Radiographic densities were measured on the films at maximum, minimum and mean surface doses of each brand of x-ray units. Results With MAX-GLS, the maximum surface doses were thirteen to fourteen times as much as the minimum surface doses. With D-60-S, the maximum surface doses were three to eight times as much as the minimum surface doses. With REX-601, the maximum surface doses were six to ten times as much as the minimum surface doses. The differences in radiographic densities among maximum, mean, and minimum doses were significant (p<0.01). Conclusion : The surface exposure doses of each x-ray machine at the same exposure parameters were different within the same manufacturer's machines.

• Journal of the Korean Society of Radiology
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• v.13 no.5
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• pp.765-771
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• 2019

Noise in skull X-ray imaging is inevitable, which reduces imaging quality and diagnostic accuracy and increases errors due to the nature of digital imaging devices. Increasing the dose can attenuate noise, but that could lead to big problems with higher exposure dose received by patients. Thus, noise reduction algorithms are actively being studied at low doses to solve dose problems and reduce noise at the same time. Wiener filter and median filter have been widely used, with the disadvantages of poor noise reduction efficiency and loss of much information about imaging boundary. The purpose of this study is to apply total variation (TV) algorithm to skull X-ray imaging that can compensate for the problems of previous noise reduction efficiency to assess quantitatively and compare them. For this study, skull X-ray imaging is obtained using various kVp and mAs using the skull phantom using the X-ray device of Siemens. In addition, contrast to noise ratio (CNR) and coefficient of variation (COV) are compared and measured when noisy image, median filter, Wiener filter and TV algorithm were applied to each phantom imaging. Experiments showed that when TV algorithms were applied, CNR and COV characteristics were excellent under all conditions. In conclusion, we've been able to see if we can use TV algorithm to improve image quality and CNR could be seen to increase due to the decrease in noise as the amount of increased mAs. On the other hand, COV decreased as the amount of increased mAs, and when kVp increased, noise was reduced and the transmittance was increased, so COV was reduced.

• 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 Radiation Protection and Research
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• v.37 no.1
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• pp.25-34
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• 2012

To know which parameters were acceptable for achieving lowest radiation exposure to the patients and highest image quality at the diagnostic X-ray radiography, we measured the patient radiation dose and image quality in transmitted PACS (Picture Archiving and Communication System) at variable combinations of the added filters. As a result, the Dose Area Product (DAP: $mGy{\cdot}cm^2$) and Entrance Surface Doses (ESDs: $mGy$) was lowest at 1 mmAl + 0.2 mmCu and highest at 0 mmAl. The histogram of the image quality by transmitted PACS was not significantly different at variable combinations of exposure parameters on the MATLAB. In conclusion, this study can be helpful for expecting radiation dose-exposure and control exposure parameters for the diagnostic X-ray radiography.

• The Journal of the Korea Contents Association
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• v.11 no.12
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• pp.357-363
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• 2011

The aim of this study is to compare radiation dose in diagnostic X-ray radiography and calculated by different mathematical equation. The result of ESDs direct measurement and that calculated by Mori NDD-M shows the biggest difference. On the other hand, equation by Edmonds shows the lowest difference of ESDs. Also, Rectification due to the difference between direct dose measurement and calculation method commutated three-phase, single phase and inverter type, show less difference in the drive way. In conclusion, this study can be helpful for expecting radiation dose-exposure and control exposure parameters for the diagnostic x-ray radiography.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.433-433
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• 2016

Carbon nanotubes (CNT) emitter has widely become an attractive mechanism that draws growing interests for cold cathode field emission. CNT yarns have demonstrated its potential as excellent field emitters. It was demonstrated that a small focal spot size was achieved by manipulating some electrical parameters, such as applied bias voltage at the mesh gate, and electrostatic focal lenses, geometrical parameters, such as axial distances of the anode, and the electrostatic focal lens from the cathode assembly, and the dimension of the opening of the electrostatic lens. Electrical-optics software was used to systematically investigate the behavior of the electron beam trajectory when the aforementioned variables were manipulated. The results of the experiment agree with the theoretical simulation results. Each variable has an individual effect on the electron beam focal spot size impinging on the target anode. An optimum condition of the parameters was obtained producing good quality of X-ray images. Also, MWCNT yarn was investigated for field emission characteristics and its contribution in the X-ray generation. The dry spinning method was used to fabricate MWCNT yarn from super MWCNTs, which was fabricated by MW-PECVD. The MWCNT yarn has a significant field emission capability in both diode and the triode X-ray generation structure compared to a MWCNT. The low-voltage-field emission of the MWCNT yarn can be attributed to the field enhancing effect of the yarn due to its shape and the contribution of the high-aspect-ratio nanotubes that protrude from the sides of the yarn. Observations of the use of filters on the development of X-ray images were also demonstrated. The amount of exposure time of the samples to the X-ray was also manipulated. The MWCNT yarn can be a good candidate for use in the low voltage field emission application of X-ray imaging.

• Journal of the Korean Society of Safety
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• v.17 no.4
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• pp.71-79
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• 2002

It was attempted to evaluate the degree of degradation of thermally aged 2.25-1Mo steek by ultrasonic monlinear parameter(UNP) measurement and X-ray diffraction analysis of extracted carbide. Artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at $540{\circ}C$. Microstructural analysis (number of carbides per unit area) and measurements of mechanical properties(Vickers hardness, DBTT) and degradation evaluation parameters(UNP and intensity ration of X-ray diffraction peak of electrolytically extracted carbide) were performed. Both of UNP and intensity ratio of X-ray diffraction peak for M6C carbide to that of M23C6 carbide(IR) increased abruptly in the initial 1000 hour of aging and then changed little. UNP and IR were proposed as potential parameters to evaluate the degree of aging degradation of 2.25Cr-1Mo steel.

• Progress in Medical Physics
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• v.32 no.1
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• pp.1-17
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• 2021

The evolution of X-ray computed tomography (CT) has been based on the discovery of X-rays, the inception of the Radon transform, and the development of X-ray digital data acquisition systems and computer technology. Unlike conventional X-ray imaging (general radiography), CT reconstructs cross-sectional anatomical images of the internal structures according to X-ray attenuation coefficients (approximate tissue density) for almost every region in the body. This article reviews the essential physical principles and technical aspects of the CT scanner, including several notable evolutions in CT technology that resulted in the emergence of helical, multidetector, cone beam, portable, dual-energy, and phase-contrast CT, in integrated imaging modalities, such as positron-emission-tomography-CT and single-photon-emission-computed-tomography-CT, and in clinical applications, including image acquisition parameters, CT angiography, image adjustment, versatile image visualizations, volumetric/surface rendering on a computer workstation, radiation treatment planning, and target localization in radiotherapy. The understanding of CT characteristics will provide more effective and accurate patient care in the fields of diagnostics and radiotherapy, and can lead to the improvement of image quality and the optimization of exposure doses.

• Journal of Radiation Protection and Research
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• v.46 no.4
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• pp.160-169
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• 2021

Background: Dual-energy X-ray images (DEI) can distinguish or improve materials of interest in a two-dimensional radiographic image, by combining two images obtained from separate low and high energies. The concepts of DEI performance describing the performance of double-exposure DEI systems in the Fourier domain been previously introduced, however, the performance of double-exposure DEI itself in terms of various parameters, has not been reported. Materials and Methods: To investigate the DEI performance, signal-difference-to-noise ratio, modulation transfer function, noise power spectrum, and noise equivalent quanta were used. Low- and high-energy were 60 and 130 kVp with 0.01-0.09 mGy, respectively. The energy-separation filter material and its thicknesses were tin (Sn) and 0.0-1.0 mm, respectively. Noise-reduction (NR) filtering used the Gaussian-filter NR, median-filter NR, and anti-correlated NR. Results and Discussion: DEI performance was affected by Sn-filter thickness, weighting factor, and dose allocation. All NR filtering successfully reduced noise, when compared with the dual-energy (DE) images without any NR filtering. Conclusion: The results indicated the significance of investigating, and evaluating suitable DEI performance, for DE images in chest radiography applications. Additionally, all the NR filtering methods were effective at reducing noise in the resultant DE images.

• Imaging Science in Dentistry
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• v.37 no.2
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• pp.65-68
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• 2007

Purpose: To compare the leakage and scattered radiation from hand-held dental X-ray unit with radiation from fixed dental X-ray unit. Materials and Methods: For evaluation we used one hand-held dental X-ray unit and Oramatic 558 (Trophy Radiologie, France), a fixed dental X-ray unit. Doses were measured with Unfors Multi-O-Meter 512L at the right and left hand levels of X-ray tube head part for the scattered and leakage radiation when human skull DXTTR III was exposed to both dental X-ray units. And for the leakage radiation only, doses were measured at the immediately right, left, superior and posterior side of the tube head part when air was exposed. Exposure parameters of handheld dental X-ray unit were 70 kVp, 3 mA, 0.1 second, and of fixed X-ray unit 70 kVp, 8 mA, 0.45 second. Results: The mean dose at the hand level when human skull DXTTR III was exposed with portable X-ray unit $6.39{\mu}Gy$, and the mean dose with fixed X-ray unit $3.03{\mu}Gy$ (p<0.001). The mean dose at the immediate side of the tube head part when air was exposed with portable X-ray unit was $2.97{\mu}Gy$ and with fixed X-ray unit the mean dose was $0.68{\mu}Gy$ (p<0.01). Conclusions: The leakage and scattered radiation from hand-held dental radiography was greater than from fixed dental radiography.