• 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.

• Journal of the Korean Society of Radiology
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• v.82 no.6
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• pp.1524-1533
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• 2021

Purpose To investigate the incidence of tuberculosis (TB) in healthcare workers (HCWs) with positive interferon-gamma release assay (IGRA) results based on chest X-ray (CXR) and CT findings and determine the role of imaging in the diagnosis of TB. Materials and Methods Among 1976 hospital personnel screened for TB using IGRA, IGRApositive subjects were retrospectively investigated. Clustered nodular and/or linear streaky opacities in the upper lung zone were considered positive on CXR. The CT findings were classified as active, indeterminate, inactive, or normal. The active or indeterminate class was considered CT-positive. Results IGRA was positive in 255 subjects (12.9%). CXR and CT were performed in 249 (99.2%) and 113 subjects (45.0%), respectively. CXR- and CT-positive findings were found in 7 of 249 (2.8%) and 9 of 113 (8.0%) patients, respectively. Among the nine CT-positive subjects, active and indeterminate TB findings were found in 6 (5.3%) and 3 (2.7%) patients, respectively. Microbiological tests, including acid-fast bacilli staining, culture, and polymerase chain reaction for TB, were negative in all nine CT-positive subjects. Empirical anti-TB medications were administered to 9 CT-positive subjects, and 3 of these nine subjects were CXR-negative for pulmonary TB.

• Journal of Biomedical Engineering Research
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• v.35 no.5
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• pp.132-141
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• 2014

In an ordinary CT scan, a large number of projections with full field-of-view (FFOV) are necessary to reconstruct high resolution images. However, excessive x-ray dosage is a great concern in FFOV scan. Region-of-interest (ROI) CT or sparse-view CT is considered to be a solution to reduce x-ray dosage in CT scanning, but it suffers from bright-band artifacts or streak artifacts giving contrast anomaly in the reconstructed image. In this study, we propose an image reconstruction method to eliminate the bright-band artifacts and the streak artifacts simultaneously. In addition to the ROI scan for the interior projection data with relatively high sampling rate in the view direction, we get sparse-view exterior projection data with much lower sampling rate. Then, we reconstruct images by solving a constrained total variation (TV) minimization problem for the interior projection data, which is assisted by the exterior projection data in the compressed sensing (CS) framework. For the interior image reconstruction assisted by the exterior projection data, we implemented the proposed method which enforces dual data fidelity terms and a TV term. The proposed method has effectively suppressed the bright-band artifacts around the ROI boundary and the streak artifacts in the ROI image. We expect the proposed method can be used for low-dose CT scans based on limited x-ray exposure to a small ROI in the human body.

• 전기의세계
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• v.38 no.8
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• pp.9-18
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• 1989

초음파 CT는 시기적으로 가장 빨리 X-ray CT와 함께 연구되어 왔으나 인체내의 투과성, 난반사, 긴파장등에 의해 실용화가 아직은 요원하다. 초음파 CT는 크게 Time of flight (TOF)CT, Attenuation CT, Reflection CT, Diffraction CT등으로 나눌수 있다. 초기에는 TOF CT, Attenuation CT의 연구가 주로 이루어 졌으나 투과의 문제로 인하여 실제로는 유방의 진단에 국한되고 있다. Reflection CT는 초음파의 특성상 실용화가 가장 쉬우나 Transducer 크기등의 문제로 연구가 지연되고 있다. Diffraction CT는 모든 초음파 CT의 특성을 갖고 있으며 현재에 실용화는 요원한 실정이다. KAIST에서는 TOF CT와 Reflection CT의 특징을 결합한 초음파 CT를 연구 발표한 바 있다. 3-D Image은 지금까지의 초음파진단장치에서 표시하는 2-D Image가 갖고 있는 제반의 문제들을 극복하기 위해 현재 KAIST에서 활발히 연구가 진행중에 있다.

• Progress in Medical Physics
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• v.21 no.1
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• pp.1-8
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• 2010

In this study, we evaluated the dose response of MAGAT (Methacrylic Acid Gelatin gel and THPC) normoxic polymer gel dosimeters based on the X-ray CT scanner. To perform this study, we determined the proper ratio of the gel composition and acquired X-ray scan parameters. MAGAT gel dosimeters were manufactured using MAA (MethacrylicAcid) and gelatin of various concentration, irradiated up to 20 Gy. We obtained the 20 CT images from the irradiated gel dosimeters by using on a Phillips Brilliance Big Bore CT scanner with the various scan parameters. This CT images were used to determine the $N_{CT}$-dose response, dose sensitivity and dose resolution As an amount of MAA and gelatin were increase, the slope and intercept were increase in each MAGAT gel dosimeter with various concentration of the $N_{CT}$-dose response curve. The dose sensitivity was $0.38{\pm}0.08$ to $0.859{\pm}0.1$ and increased were amount of the MAA was increased or the gelatin was decreased. However, the change of gelatin concentration was very small compare to MAA. The Dose resolution ($D_{\Delta}^{95%}$) varies considerably from 2.6 to 6 Gy, dependent on dose resolution and CT image noise. The slope and dose sensitivity was almost ident verywith the variation of the tube voltage, tube current and slice thickness in the dose response curve, but the noise (standard deviation of averamalg CT number) was decreased when the tube voltage, tube current and slice thickness are increase. The optimal MAGAT polymer gel dosimeter based on the CT were evaluated to determine the CT imaging scan parameters of the maximum tube voltage, tube current and slice thickness (commonly used in clinical) using the composition ratio of a 9% MAA, 8% gelatin and 83% water. This study could get proper composition ratio and scan parameter evaluating dose response of MAGAT normoxic polymer gel dosimeter using CT scanner.

• Proceedings of the Korean Society of Radiological Science
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• 1991.05a
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• pp.11.2-11.2
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• 1991

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.468-470
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• 2002

We have designed X-ray detection system and multi-channel data acquisition system for Spiral CT application. X-ray detection system consists of scintillator and photodiode. Scintillator converts X-ray into visible light. Photodiode converts visible light into electrical signal. The multi-channel data acquisition system consists of analog, digital, master and backplane board. Analog board detects electrical signal and amplifies signal by 140dB. Digital board consists of MUX(Multiplex) which routes multi-channel analog signal to preamplifier, and ADC(Analog to Digital Converter) which converts analog signal into digital signal. Master board supplies the synchronized clock and transmits the digital data to image reconstructor. Backplane provides electrical power, analog output and clock signal. The system converts the projected X-ray signal over the detector array with large gain, samples the data in each channel sequentially, and the sampled data are transmitted to host computer in a given time frame. To meet the timing limitation, this system is very flexible since it is implemented by FPGA(Field Programmable Gate Array). This system must have a high-speed operation with low noise and high SNR(signal to noise ratio), wide dynamic range to get a high resolution image.

• Composites Research
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• v.22 no.6
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• pp.13-17
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• 2009

This paper decided the 3D shape of sandwich composite for the cradle of CT instrument, suggested the stacking sequence with satisfaction on structural criteria using the Finite Element Analysis, and introduced the manufacturing method to meet the X-ray transmission performance uniformly. The design of Cradle was considered the space between other parts, fixing method, and assembly condition with headrest part. It is decided the stacking sequence to meet the criteria that the deflection at the end point is less than 20 mm when it is applied to 135 kg load at the specific locations. In site of manufacturing method, at first, it is used the hand lay-up for carbon UD and carbon fabric/polyester resin, but it had the ununiform X-ray transmission performance due to the void and excess resin. For solving this problem, it was replaced with the infusion method for the first layer of face material and the application of carbon UD or fabric/epoxy resin prepreg for other layers. Therefor, the property of X-ray transmission was improved.

• Journal of the Korean Society of Radiology
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• v.13 no.7
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• pp.1015-1024
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• 2019

In the medical field, X-rays are essential in the diagnosis and treatment of diseases, and the use of X-rays continues to increase with the development of imaging technology, but X-rays have the disadvantage of radiation exposure. Although lead protection tools are used in clinical practice to protect against radiation exposure, lead is classified as a heavy metal and can cause harmful reactions such as lead poisoning. Therefore, the purpose of this study is to investigate the usefulness of the shield fabricated using materials of FDM (Fused Deposition Modeling) 3D printer. In order to confirm the filament's line attenuation factor, phantoms were fabricated using PLA, XT-CF20, Wood, Glow and Brass, and CT scan was performed. And the shielding sheet of 100 × 100 × 2 mm size was modeled, the dose and shielding rate was measured by using a diagnostic X-ray generator and irradiation dose meter, and the shielding rate with lead protection tools. As a result of the experiment, the CT number of the brass was measured to be the highest, and the shielding sheet was manufactured by using the brass. As a result of confirming with the diagnostic X-ray generator, the shielding rate was increased in the shielding sheet having a thickness of 6 mm upon X-ray irradiation under the condition of 100 kV and 40 mAs. It measured by 90% or more, and confirmed that the shielding rate is higher than apron 0.25 mmPb. As a result of this study, it was confirmed that the shield fabricated by 3D printing technology showed high shielding rate in the diagnostic X-ray region. there was.

• The Korean Journal of Nuclear Medicine Technology
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• v.17 no.2
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• pp.10-14
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• 2013

Purpose: Due to developed simultaneous PET/MRI, it has become possible to obtain more anatomical image information better than conventional PET/CT. By the way, in the PET/CT, the linear absorption coefficient is measured by X-ray directly. However in case of PET/MRI, the value is not measured from MRI images directly, but is calculated by dividing as 4 segmentation ${\mu}-map$. Therefore, in this paper, we will evaluate the SUV's difference of attenuation correction PET images from PET/MRI and PET/CT. Materials and Methods: Biograph mCT40 (Siemens, Germany), Biograph mMR were used as a PET/CT, PET/MRI scanner. For a phantom study, we used a solid type $^{68}Ge$ source, and a liquid type $^{18}F$ uniformity phantom. By using VIBE-DIXON sequence of PET/MRI, human anatomical structure was divided into air-lung-fat-soft tissue for attenuation correction coefficient. In case of PET/CT, the hounsfield unit of CT was used. By setting the ROI at five places of each PET phantom images that is corrected attenuation, the maximum SUV was measured, evaluated %diff about PET/CT vs. PET/MRI. In clinical study, the 18 patients who underwent simultaneous PET/CT and PET/MRI was selected and set the ROI at background, lung, liver, brain, muscle, fat, bone from the each attenuation correction PET images, and then evaluated, compared by measuring the maximum SUV. Results: For solid $^{68}Ge$ source, SUV from PET/MRI is measured lower 88.55% compared to PET/CT. In case of liquid $^{18}F$ uniform phantom, SUV of PET/MRI as compared to PET/CT is measured low 70.17%. If the clinical study, the background SUV of PET/MRI is same with PET/CT's and the one of lung was higher 2.51%. However, it is measured lower about 32.50, 40.35, 23.92, 13.92, 5.00% at liver, brain, muscle, fat, femoral head. Conclusion: In the case of a CT image, because there is a linear relationship between 511 keV ${\gamma}-ray$ and linear absorption coefficient of X-ray, it is possible to correct directly the attenuation of 511 keV ${\gamma}-ray$ by creating a ${\mu}$map from the CT image. However, in the case of the MRI, because the MRI signal has no relationship at all with linear absorption coefficient of ${\gamma}-ray$, the anatomical structure of the human body is divided into four segmentations to correct the attenuation of ${\gamma}-rays$. Even a number of protons in a bone is too low to make MRI signal and to localize segmentation of ${\mu}-map$. Therefore, to develope a proper sequence for measuring more accurate attenuation coefficient is indeed necessary in the future PET/MRI.