• Progress in Medical Physics
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• v.22 no.4
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• pp.163-171
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• 2011

The purpose of this study was to investigate the effect of various technical parameters for the dose optimization in pediatric chest radiological examinations by evaluating effective dose and effective detective quantum efficiency (eDQE) including the scatter radiation from the object, the blur caused by the focal spot, geometric magnification and detector characteristics. For the tube voltages ranging from 40 to 90 kVp in 10 kVp increments at the FDD of 100, 110, 120, 150, 180 cm, the eDQE was evaluated at the same effective dose. The results showed that the eDQE was largest at 60 kVp when compares the eDQE at different tube voltage. Especially, the eDQE was considerably higher without the use of an anti-scatter grid on equivalent effective dose. This indicates that the reducing the scatter radiation did not compensate for the loss of absorbed effective photons in the grid. When the grid is not used the eDQE increased with increasing FDD because of the greater effective modulation transfer function (eMTF). However, most of major hospitals in Korea employed a short FDD of 100 cm with an anti-scatter grid for the chest radiological examination of a 15 month old infant. As a result, the entrance surface air kerma (ESAK) values for the hospitals of this survey exceeded the Korean DRL (diagnostic reference level) of $100{\mu}Gy$. Therefore, appropriate technical parameters should be established to perform pediatric chest examinations on children of different ages. The results of this study may serve as a baseline to establish detailed reference level of pediatric dose for different ages.

• Progress in Medical Physics
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• v.6 no.2
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• pp.71-81
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• 1995

Consecutive brain 〔Tc-99m〕ECD SPECT studies before and after acetazolamide (Diamox) administration have been performed with patients for the evaluation of cerebrovascular hemodynamic reserve. However, the quantitaitve potential of SPECT Diamox imaging is limited as a result of degrading fractors such as finite detector resolution, attenuation, scatter, poor counting statistics, and methods of data analysis. Making physical measurements in phantoms filled with known amounts of radioactivity can help characterize and potentially quantify the sensitivities. However, it is often very difficult to make a realistic phantom simulating patients in clinical situations. By computer simulation, we studied the sensitivities of ECD SPECT before and after Diamox administration. The sensitivity is defined as ($\Delta$N/N)/($\Delta$S/S)$\times$100％, where $\Delta$N denotes the differences in mean counts between post-and pre-Diamox in the measured data, N denotes the mean counts before Diamox in the measure data, $\Delta$S denotes the differences in mean counts between post-and pre-Diamox in the model, and S denotes the mean counts before Diamox in the model. In clinical Diamox studies, the percentage changes of radioactivity could be determined to measure changes in radioactivity concentration by Diamox after subtracting pre-from post-Diamox data. However, the optimal amount of subtraction for 100％ sensitivity is not known since this requires a thorough sensitivity analysis by computer simulation. For consecutive brain SPECT imaging model before and after Diamox, when 30％ increased radioactivity concentrations were assingned for Diamox effect in model, the sensitivities were measured as 51.03, 73.4, 94.00, 130.74％ for 0, 100, 150, 200％ subtraction, respectively. Sensitivity analysis indicated that the partial voluming effects due to finite detector resolution and statistical noise result in a significant underestimation of radioactivity measurements and the amount of underestimation depends on the. ％ increase of radioactivity concentration and ％ subtraction of pre-from post-Diamox data. The 150％ subtraction appears to be optimal in clinical situations where we expect approximately 30％ changes in radioactivity concentration. The computer simulation may be a powerful technique to study sensitivities of ECD SPECT before and after Diamox administration.

• The Korean Journal of Nuclear Medicine Technology
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• v.15 no.1
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• pp.58-64
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• 2011

Objective: The 3-dimensional reconstruction method with resolution recovery modeling has advantages of high spatial resolution and contrast because of its precise modeling of spatial blurring according to the distance from detector plane. The aim of this study was to evaluate one of the resolution recovery reconstruction methods (Astonish, Philips Medical), compare it to other iterative reconstructions, and verify its clinical usefulness. Materials and Methods: NEMA IEC PET body phantom and Flanges Jaszczak ECT phantom (Data Spectrum Corp., USA) studies were performed using Skylight SPECT (Philips) system under four different conditions; short or long (2 times of short) radius, and half or full (40 kcts/frame) acquisition counts. Astonish reconstruction method was compared with two other iterative reconstructions; MLEM and 3D-OSEM which vendor supplied. For quantitative analysis, the contrast ratios obtained from IEC phantom test were compared. Reconstruction parameters were determined by optimization study using graph of contrast ratio versus background variability. The qualitative comparison was performed with Jaszczak ECT phantom and human myocardial data. Results: The overall contrast ratio was higher with Astonish than the others. For the largest hot sphere of 37 mm diameter, Astonish showed about 27.1% and 17.4% higher contrast ratio than MLEM and 3D-OSEM, in short radius study. For long radius, Astonish showed about 40.5% and 32.6% higher contrast ratio than MLEM and 3D-OSEM. The effect of acquired counts was insignificant. In the qualitative studies with Jaszczak phantom and human myocardial data, Astonish showed the best image quality. Conclusion: In this study, we have found out that Astonish can provide more reliable clinical results by better image quality compared to other iterative reconstruction methods. Although further clinical studies are required, Astonish would be used in clinics with confidence for enhancement of images.

• Radiation Oncology Journal
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• v.20 no.4
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• pp.396-404
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• 2002

Purpose : Many papers support a correlation between rectal complications and rectal doses in uterine cervical cancer patients treated with radical radiotherapy. In vivo dosimetry in the rectum following the ICRU report 38 contributes to the quality assurance in HDR brachytherapy, especially in minimizing side effects. This study compares the rectal doses calculated in the radiation treatment planning system to that measured with a silicon diode the in vivo dosimetry system. Methods : Nine patients, with a uterine cervical carcinoma, treated with Iridium-192 high dose rate brachytherapy between June 2001 and Feb. 2002, were retrospectively analysed. Six to eight-fractions of high dose rate (HDR)-intracavitary radiotherapy (ICR) were delivered two times per week, with a total dose of $28\~32\;Gy$ to point A. In 44 applications, to the 9 patients, the measured rectal doses were analyzed and compared with the calculated rectal doses using the radiation treatment planning system. Using graphic approximation methods, in conjunction with localization radiographs, the expected dose values at the detector points of an intrarectal semiconductor dosimeter, were calculated. Results : There were significant differences between the calculated rectal doses, based on the simulation radiographs, and the calculated rectal doses, based on the radiographs in each fraction of the HDR ICR. Also, there were significant differences between the calculated and measured rectal doses based on the in-vivo diode dosimetry system. The rectal reference point on the anteroposterior line drawn through the lower end of the uterine sources, according to ICRU 38 report, received the maximum rectal doses in only 2 out of the nine patients $(22.2\%)$. Conclusion : In HDR ICR planning for conical cancer, optimization of the dose to the rectum by the computer-assisted planning system, using radiographs in simulation, is improper. This study showed that in vivo rectal dosimetry, using a diode detector during the HDR ICR, could have a useful role in quality control for HDR brachytherapy in cervical carcinomas. The importance of individual dosimeters for each HDR ICR is clear. In some departments that do not have the in vivo dosimetry system, the radiation oncologist has to find, from lateral fluoroscopic findings, the location of the rectal marker before each fractionated HDR brachytherapy, which is a necessary and important step of HDR brachytherapy for cervical cancer.

• Journal of the Korean Chemical Society
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• v.63 no.4
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• pp.246-252
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• 2019

In the system of GC-OTC/FID (Gas chromatography-Open Tubular Column/Flame Ionization Detector), DMSO (Dimethyl sulfide) solvent was used to separate the polar solvents (Alcohols). In this system DMSO was eluted later than the separated polar solvents. At this system to calculate chromatographic factors [adjusted retention time ($t_R^{\prime}=t_R-t_O$), capacity factor{$k^{\prime}=(t_R-t_O)/t_O$} and separation factor {${\alpha}=(t_{R2}-t_O)/(t_{R1}-t_O)$}], dead time($t_O$) is necessary, but the method to calculate it has not been reported yet. Therefore, we have tried to develop $t_O$. To calculate $t_O$, we conversed DMSO retention time (DMSO $t_R$) to logarithm ($f(x)={\log}\;t_{R(DMSO)}{\rightarrow}t_O$, $t_O={\log}$ 9.551=0.980). To confirm the optimization of the developed method, we compared with $CH_4\;t_R$ and ${\ln}\;t_{R(DMSO)}$. Both of the values calculated by $CH_4\;t_R$ and ${\ln}\;t_{R(DMSO)}$ were not suitable in the calculation k' and ${\alpha}$. The developed method in this study{${\log}\;t_{R(DMSO)}$} has satisfied both of the values k' criteria (1${\alpha}(1<{\alpha}<2)$. The developed calculation method in this study was easy and convenient, therefore it can be expected to be applied to these similar systems.

• Korean Journal of Food Science and Technology
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• v.36 no.4
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• pp.531-536
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• 2004

Synthesis conditions were optimized using response surface methodology for producing structured lipids (SL) by interesterification of DHA-enriched algae oil derived from microalgae, Schizochytrium sp. and corn oil. Reaction was performed fer 24 hr at $55^{\circ}C$ catalyzed by immobilized lipase from Rhizomucor miehei (RM IM) in shaking water bath. Major fatty acids of SL were palmitic (21.70 mol%), oleic (20.20 mol%), and linoleic (27.34 mol%) acids, and DHA (15.06 mol%). To separate newly synthesized SL-triglycerides (TG) species, HPLC with evaporative light scatting detector (ELSD) was used. Production conditions were optimized using central composite design with reaction temperature $(35-75^{\circ}C,\;X_1)$, reaction time $(2-42\;hr,\;X_2)$, and enzyme concentration $(2-14%,\;X_3)$ as variables. When variables were $70.28^{\circ}C\;(X_1),\;28.74\;hr\;(X_2),\;and\;11.30%\;(X_3)$, maximum content of selected three peaks of synthesized SL-TG species was predicted as 6.97 area%.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.1
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• pp.35-41
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• 2014

Trihalomethanes (THMs) are formed as a results of the reaction of residual chlorine, used as a disinfectant in drinking water, with the organic matter in raw water. Although chlorinated and brominated THMs are the most common disinfection byproducts (DBPs) reported, iodinated THMs (I-THMs) can be formed when iodide is present in raw water. I-THMs have been usually associated with several medicinal or pharmaceutical taste and odor problems and is a potential health concern since they have been reported to be more toxic than their brominated and chlorinated analogs. Currently, there is no published standard analytical method for I-THMs in water. An automated headspace-gas chromatography/electron capture detector (GC/ECD) technique was developed for routine analysis of 10 THMs including 6 I-THMs in water samples. The optimization of the method is discussed. The limits of detection (LOD) and limits of quantification (LOQ) range from 12 ng/L to 56 ng/L and from 38 ng/L to 178 ng/L for 10 THMs, respectively. Matrix effects in river water, sea water and wastewater treatment plant (WWTP) final effluent water were investigated and it was shown that the method is suitable for the analysis of trace levels of I-THMs, in a wide range of waters. The method developed in the present study has the advantage of being rapid, simple and sensitive.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.4
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• pp.11-23
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• 2011

The objective of this paper is to develop a daily pattern clustering algorithm using historical traffic data that can reliably detect under various traffic flow conditions in urban streets. The developed algorithm in this paper is categorized into two major parts, that is to say a macroscopic and a microscopic points of view. First of all, a macroscopic analysis process deduces a daily peak/non-peak hour and emphasis analysis time zones based on the speed time-series. A microscopic analysis process clusters a daily pattern compared with a similarity between individuals or between individual and group. The name of the developed algorithm in microscopic analysis process is called "Two-step speed clustering (TSC) algorithm". TSC algorithm improves the accuracy of a daily pattern clustering based on the time-series speed variation data. The experiments of the algorithm have been conducted with point detector data, installed at a Ansan city, and verified through comparison with a clustering techniques using SPSS. Our efforts in this study are expected to contribute to developing pattern-based information processing, operations management of daily recurrent congestion, improvement of daily signal optimization based on TOD plans.

• Journal of the Korean Society of Radiology
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• v.17 no.1
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• pp.1-9
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• 2023

For optimal image quality of computer tomography angiography (CTA), different iodine concentrations and scan parameters were applied to quantitatively evaluate the image quality characteristics of filtered back projection (FBP), hybrid-iterative reconstruction (hybrid-IR), and deep learning reconstruction (DLR). A 320-row-detector CT scanner scanned a phantom with various iodine concentrations (1.2, 2.9, 4.9, 6.9, 10.4, 14.3, 18.4, and 25.9 mg/mL) located at the edge of a cylindrical water phantom with a diameter of 19 cm. Data obtained using each reconstruction technique was analyzed through noise, coefficient of variation (COV), and root mean square error (RMSE). As the iodine concentration increased, the CT number value increased, but the noise change did not show any special characteristics. COV decreased with increasing iodine concentration for FBP, adaptive iterative dose reduction (AIDR) 3D, and advanced intelligent clear-IQ engine (AiCE) at various tube voltages and tube currents. In addition, when the iodine concentration was low, there was a slight difference in COV between the reconstitution techniques, but there was little difference as the iodine concentration increased. AiCE showed the characteristic that RMSE decreased as the iodine concentration increased but rather increased after a specific concentration (4.9 mg/mL). Therefore, the user will have to consider the characteristics of scan parameters such as tube current and tube voltage as well as iodine concentration according to the reconstruction technique for optimal CTA image acquisition.

• Korean Journal of Food Science and Technology
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• v.33 no.1
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• pp.33-39
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• 2001

To develop a method for separation process using Sep-pak $C_18$, simultaneous and systematic analysis of 8 permitted and 11 non-permitted synthetic food colors in Korea, optimization of analysis conditions for reverse phase ion-pair high performance liquid chromatography was carried out. For the best result of Sep-pak $C_18$ separation the pH of color standard mixture solution was $5{\sim}6$ and 0.1% HCl-methanol solution were set as eluent. The colors eluated from Sep-pak $C_18$ cartridge were determined and confirmed by high performance liquid chromatography with a photodiode array detector at 420 nm for yellow colors type, at 520 nm for red colors type, at 600 nm for blue and green colors type and at 254 nm for mixed colors. Conditions for HPLC analysis were as follows: column, Symmetry $C_18$ (5 m, 3.9 mm $i.d.{\times}150\;mm$); mobile phase, 0.025 M ammonium acetate (containing 0.01 M tetrabutylammonium bromide) : acetonitrile : methanol (65 : 25 : 10) and 0.025 M ammonium acetate(containing 0.01 M tetrabutylammonium bromide) : acetonitrile : methanol (40 : 50 : 10); flow rate, 1 mL/min. It takes 35 minutes for simultaneaus analysis and 18 minutes for systematic analysis. The detection limits range of each colors were $0.01{\sim}0.05\;{\mu}g/g$.