• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.189-195
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• 2023

As a PEMFC (Polymer Exchange Membrane Fuel Cell) cathode catalyst, Pt-Co/C has recently been widely used because of its improved durability. In a fuel cell, electrodes and electrolytes have a close influence on each other in terms of performance and durability. The effect on the electrochemical durability of the electrolyte membrane when Pt-Co/C was replaced in the Pt/C electrode catalyst was studied. The durability of Pt-Co/C MEA (Membrane Electrode Assembly) was higher than that of Pt/C MEA in the electrochemical accelerated degradation process of PEMFC membrane. As a result of analyzing the FER (Fluorine Emission Rate) and hydrogen permeability, it was shown that the degradation rate of the membrane of Pt-Co/C MEA was lower than that of Pt/C MEA. In the OCV (Open Circuit Voltage) holding process, the rate of decrease of the active area of the Pt-Co/C electrode was lower than that of the Pt/C electrode, and the amount of Pt deposited on the membrane was smaller in Pt-Co/C MEA than in Pt/C MEA. Pt inside the polymer membrane deteriorates the membrane by generating radicals, so the degradation rate of the membrane of Pt/C MEA with a high Pt deposition rate was higher than Pt-Co/C MEA. When the Pt-Co/C catalyst was used, the electrode durability was improved, and the amount of Pt deposited on the membrane was also reduced, thereby improving the electrochemical durability of the membrane.

• The Korean Journal of Nuclear Medicine Technology
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• v.27 no.2
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• pp.111-127
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• 2023

Purpose: Gallium-68 (⁶⁸Ga) is increasingly used in nuclear medicine imaging for various conditions such as lymphoma and neuroendocrine tumors by labeling tracers like Prostate Specific Membrane Antigen (PSMA) and DOTA-TOC. However, compared to Fluorine-18 (¹⁸F) used in conventional nuclear medicine imaging, ⁶⁸Ga has lower spatial resolution and relatively higher Signal to Background Ratio (SBR). Therefore, this study aimed to investigate the optimized parameters and reconstruction methods for PET/CT imaging using the ⁶⁸Ga radiotracer through model-based image evaluation. Materials and Methods: Based on clinical images of ⁶⁸Ga-PSMA PET/CT, a NEMA/IEC 2008 PET phantom model was prepared with a Hot vs Background (H/B) ratio of 10:1. Images were acquired for 9 minutes in list mode using DMIDR (GE, Milwaukee WI, USA). Subsequently, reconstructions were performed for 1 to 8 minutes using OS-EM (Ordered Subset Expectation Maximization) + TOF (Time of Flight) + Sharp IR (VPFX-S), and BSREM (Block Sequential Regularized Expectation Maximization) + TOF + Sharp IR (QCFX-S-400), followed by comparative evaluation. Based on the previous experimental results, images were reconstructed for BSREM + TOF + Sharp IR / 2 minutes (QCFX-S-2min) with varying β-strength values from 100 to 700. The image quality was evaluated using AMIDE (freeware, Ver.1.0.1) and Advanced Workstation (GE, USA). Results: Images reconstructed with QCFX-S-400 showed relatively higher values for SNR (Signal to Noise Ratio), CNR (Contrast to Noise Ratio), count, RC (Recovery Coefficient), and SUV (Standardized Uptake Value) compared to VPFX-S. SNR, CNR, and SUV exhibited the highest values at 2 minutes/bed acquisition time. RC showed the highest values for a 10 mm sphere at 2 minutes/bed acquisition time. For small spheres of 10 mm and 13 mm, an inverse relationship between β-strength increase and count was observed. SNR and CNR peaked at β-strength 400 and then decreased, while SUV and RC exhibited a normal distribution based on sphere size for β-strength values of 400 and above. Conclusion: Based on the experiments, PET/CT imaging using the ⁶⁸Ga radiotracer yielded the most favorable quantitative and qualitative results with a 2 minutes/bed acquisition time and BSREM reconstruction, particularly when applying β-strength 400. The application of BSREM can enhance accurate quantification and image quality in ⁶⁸Ga PET/CT imaging, and an optimization process tailored to each institution's imaging objectives appears necessary.

• Korean Journal of Clinical Laboratory Science
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• v.55 no.4
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• pp.261-268
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• 2023

[¹⁸F]Fluorocholine is a radiopharmaceutical used non-invasively in positron emission tomography to diagnose parathyroid adenoma, prostate cancer, and hepatocellular carcinoma by evaluating the choline metabolism. In this study, a radiolabeling method for [¹⁸F]fluorocholine was optimized using a solid phase extraction (SPE) cartridge. [¹⁸F]Fluorocholine was labeled in two steps using an automated synthesizer. In the first step, dibromomethane was reacted with [¹⁸F]KF/K2.2.2/K₂CO₃ to obtain the intermediate [¹⁸F]fluorobromomethane. In the second step, [¹⁸F]fluorobromomethane was passed through a Sep-Pak^Ⓡ Silica SPE cartridge to remove the impurities and then reacted with N,N-dimethylaminoethanol (DMAE) in a Sep-Pak^Ⓡ C18 SPE cartridge to label [¹⁸F]fluorocholine. The reaction conditions of [¹⁸F]fluorocholine were optimized. The synthesis yield was confirmed according to the number of silica cartridges and DMAE concentration. No statistically significant difference in the synthesis yield of [¹⁸F]fluorocholine was observed when using four or three silica cartridges (P>0.05). The labeling yield was 11.5±0.5% (N=4) when DMAE was used as its original solution. On the other hand, when diluted to 10% with dimethyl sulfoxide, the radiochemical yield increased significantly to 30.1±5.2% (N=20). In conclusion, [¹⁸F]Fluorocholine for clinical use can be synthesized stably in high yield by applying an optimized synthesis method.

• Korean Journal of Radiology
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• v.20 no.4
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• pp.671-682
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• 2019

Objective: To investigate whether computed tomography (CT) and fluorine-18-labeled fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) may be applied to distinguish thymic epithelial tumors (TETs) from benign cysts in the anterior mediastinum. Materials and Methods: We included 262 consecutive patients with pathologically proven TETs and benign cysts 5 cm or smaller who underwent preoperative CT scans. In addition to conventional morphological and ancillary CT findings, the relationship between the lesion and the adjacent mediastinal pleura was evaluated qualitatively and quantitatively. Mean lesion attenuation was measured on CT images. The maximum standardized uptake value (SUVmax) was obtained with FDG-PET scans in 40 patients. CT predictors for TETs were identified with multivariate logistic regression analysis. For validation, we assessed the diagnostic accuracy and inter-observer agreement between four radiologists in a size-matched set of 24 cysts and 24 TETs using a receiver operating characteristic curve before and after being informed of the study findings. Results: The multivariate analysis showed that post-contrast attenuation of 60 Hounsfield unit or higher (odds ratio [OR], 12.734; 95% confidence interval [CI], 2.506-64.705; p = 0.002) and the presence of protrusion from the mediastinal pleura (OR, 9.855; 95% CI, 1.749-55.535; p = 0.009) were the strongest CT predictors for TETs. SUVmax was significantly higher in TETs than in cysts (5.3 ± 2.4 vs. 1.1 ± 0.3; p < 0.001). After being informed of the study findings, the readers' area under the curve improved from 0.872-0.955 to 0.949-0.999 (p = 0.066-0.149). Inter-observer kappa values for protrusion were 0.630-0.941. Conclusion: Post-contrast CT attenuation, protrusion from the mediastinal pleura, and SUVmax were useful imaging features for distinguishing TETs from cysts in the anterior mediastinum.

• The Journal of Engineering Geology
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• v.19 no.4
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• pp.529-541
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• 2009

Hydrochemical, stable isotopic ($\delta^{18}O$ and dD) and noble gas isotopic analyses of seven hot spring water samples, eleven groundwater samples and six surface water samples collected from the Icheon and Pocheon area were carried out to find out hydrochemical characteristics, and to interpret the source of noble gases and the geochemical evolution of the hot spring waters. The hot spring waters show low temperature type ranging from 21.5 to $31.4^{\circ}C$ and the pH value between 6.69 and 9.21. Electrical conductivity of hot spring waters has the range from 310 to $735\;{\mu}S/cm$. Whereas the hot spring water in the Icheon area shows the geochemical characteristics of neutral pH, the $Ca-HCO_3$(or $Ca(Na)-HCO_3$) chemical type and a high uranium content, the hot spring water in the Pocheon area shows the characteristics of alkaline pH, the $Na-HCO_3$ chemical type and a high fluorine content. These characteristics indicate that the hot spring water in the Icheon area is under the early stage in the geochemical evolution, and that the hot spring water in the Pocheon area has been geochemically evolved. The $\delta^{18}O$ and ${\delta}D$ values of hot spring waters show the range of $-10.1{\sim}-8.69%o$ and from $-72.2{\sim}-60.8%o$, respectively, and these values supply the information of the recharge area of hot spring waters. The $^3He/^4He$ ratios of the hot spring waters range from $0.09\;{\times}\;10^{-6}$ to $0.65\;{\times}\;10^{-6}$ which are plotted above the mixing line between air and crustal components. Whereas the helium gas in the Icheon hot spring water was mainly provided from the atmospheric source mixing with the mantle(or magma) origin, the origin of helium gas in the Pocheon hot spring water shows a dominant crustal source. $^{40}Ar/^{36}Ar$ ratios of hot spring water are in the range of an atmosphere source.

• Journal of dental hygiene science
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• v.9 no.3
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• pp.287-294
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• 2009

The purpose of this survey research was to investigation the relationship among dental health state, care and knowledge of patients who participate in dental hygiene process of dental hygiene students voluntarily. And the following conclusion were obtained from questionnaires for 266 volunteers using SPSSWIN 12.0. 1. For the dental health state according to sex distinction, it showed that women (DMFT index: 13.0) was higher than men (DMFT index: 10.4) and statistically significant difference. For DT rate, men (32.0) was higher than women (30.0), for MT rate men (32.2) was higher than women (26.6) and it showed statistically significant difference (P<0.05). 2. For the dental health knowledge according to sex distinction, 77.8% patients replied as the food causing teeth decay are chocolate, biscuits, etc. and it didn't showed significant difference statistically. 72.4% men and 84.7% women replied as they could take precautions against a dental caries using fluorine and it showed statistically significant difference(P<0.05). 3. For brushing their teeth from top to down for the upper tooth and from down to top for the lower one, 80.3% patients replied as they did like that but 62.5% patients as they didn't. And 68.2% patients replied as the food causing teeth decay arc chocolate, biscuits, etc. and 81.0% patients didn't like that. It showed statistically significant difference. (P<0.05) 4. 50.5% patients went to the dental hospital once per 6 month and it showed statistically significant difference. And 71.3% patients replied as the food causing teeth decay are chocolate, biscuits, etc. and 81.0% patients didn't like that, It showed statistically significant difference. (P<0.05)

• Journal of Food Hygiene and Safety
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• v.23 no.2
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• pp.98-107
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• 2008

The ozone has the oxidizing power which is powerful the fluorine and the antimicrobial spectrum of wide scope. Researches were carried out to use the merits that ozone has in various fields including the food industry, and many studies are also conducted nowadays for more efficient use of ozone. The ozone was permitted legally as a food additive and was practically used in the United States, Australia, Japanese etc. In November 2007, ozone water was permitted as a food additive in Korea and the interest in the use of ozone water has been on the rise in the Korea's food industry. As a olisinfectant method, ozone has many advantages. The maintenance and management expenses of ozone are lower than the installation cost at early stages and no by-products are generated after use it compared to others. Recently the demand of ozone as a olisinfectant method is increasing drastically. Although ozone water is popularly used to sterilize raw foods like fruits, vegetables and meats, the cases are still limited and were verified by the survey results. However, the use of ozone water is gradually being increased and is focused on food services. Ozone water refers to a state where ozone is dissolved into water to more conveniently use ozone. Accordingly, ozone water should be managed in regards with the amount and time of water-dissolved ozone, and the control of discharged ozone concentration is required for safe use of ozone water. The items to control mentioned above are directly related to the performance of the devices, and therefore, it is required to newly establish the performance criteria of ozone water manufacturing devices.

• The Korean Journal of Nuclear Medicine Technology
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• v.14 no.2
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• pp.104-109
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• 2010

Purpose: $[^{18}F]$Fallypride plays an effective radiotracer for the study of dopamine $D_2/D_3$ receptor occupancy, neuropsychiatric disorders and aging in humans. This tracer has the potential for clinical use, but automated labeling efficiency showed low radiochemical yields about 5~20% with relatively long labelling time of fluorine-18. In present study, we describe an improved automatic synthesis of [$^{18}F$]Fallypride using different base concentration for routine clinical use. Materials and Methods: Fully automated synthetic process of [$^{18}F$]Fallypride was perform using the TracerLab $FX_{FN}$ synthesizer under various labeling conditions and tosyl-fallypride was used as a precursor. [$^{18}F$]Fluoride was extracted with various concentration of $K_{2.2.2.}/K_2CO_3$ from $^{18}O$-enriched water trapped on the ion exchange cartridge. After azeotropic drying, the labeling reaction proceeded in $CH_3CN$ at $100^{\circ}C$ for 10 or 30 min. The reaction mixture was purified by reverse phase HPLC and collected organic solution was exchanged by tc-18 Sep-Pak for the clinically available solution. Results: The optimal labeling condition of [$^{18}F$]Fallypride in the automatic production was that 2 mg of tosyl-fallypride in acetonitrile (1 mL) was incubated at $100^{\circ}C$ for 10 min with $K_{2.2.2.}/K_2CO_3$ (11/0.8 mg). [$^{18}F$]Fallypride was obtained with high radiochemical yield about $66{\pm}1.4%$ (decay-corrected, n=28) within $51{\pm}1.2$ min including HPLC purification and solid-phase purification for the final formulation. Conclusion: [$^{18}F$]Fallypride was prepared with a significantly improved radiochemical yield with high specific activity and shorten synthetic time. In addition, this automated procedure provides the high reproducibility with no synthesis failures (n=28).

• The Korean Journal of Nuclear Medicine Technology
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• v.22 no.1
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• pp.51-54
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• 2018

Purpose $^{18}F-THK5351$ is the newly developed PET probe for tau imaging in alzheimer's disease. The purpose of study was to establish the automated production of $^{18}F-THK5351$ on a commercial module. Materials and Methods Two different approaches were evaluated for the synthesis of $^{18}F-THK5351$. The first approach (method I) included the nucleophilic $^{18}F$-fluorination of the tosylate precursor, subsequently followed by pre-HPLC purification of crude reaction mixture with SPE cartridge. In the second approach (method II), the crude reaction mixture was directly introduced to a semi-preparative HPLC without SPE purification. The radiosynthesis of $^{18}F-THK5351$ was performed on a commercial GE $TRACERlab^{TM}$ $FX-_{FN}$ module. Quality control of $^{18}F-THK5351$ was carried out to meet the criteria guidelined in USP for PET radiopharmaceuticals. Results The overall radiochemical yield of method I was $23.8{\pm}1.9%$ (n=4) as the decay-corrected yield (end of synthesis, EOS) and the total synthesis time was $75{\pm}3min$. The radiochemical yield of method II was $31.9{\pm}6.7%$ (decay-corrected, n=10) and the total preparation time was $70{\pm}2min$. The radiochemical purity was>98%. Conclusion This study shows that method II provides higher radiochemical yield and shorter production time compared to the pre-SPE purification described in method I. The $^{18}F-THK5351$ synthesis by method II will be ideal for routine clinical application, considering short physical half-life of fluorine-18 ($t_{1/2}=110min$).

• The Korean Journal of Nuclear Medicine
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• v.33 no.5
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• pp.439-451
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• 1999

Purpose : It is important to differentiate malignant from benign lesions of intraocular masses in choosing therapeutic plan. Biopsy of intraocular tumor is not recommended due to the risk of visual damage. We evaluated the usefulness of F-18-FDG PET imaging in diagnosing intraocular neoplasms. Materials and Methods: F-18-FDG PET scan was performed in 13 patients (15 lesions) suspected to have malignant intraocular tumors. There were 3 benign lesions (retinal detachment, choroidal effusion and hemorrhage) and 10 patients with 12 malignant lesions (3 melanomas, 7 retinoblastomas and 2 metastatic cancers). Regional eye images ($256{\times}256$ and $128{\times}128$ matrices) were obtained with or without attenuation correction. Whole body scan was also performed in eight patients (3 benign and 6 malignant lesions). Results: All malignant lesions were visualized while all benign lesions were not visualized. The mean peak standardized uptake value (SUV) of malignant lesions was $2.64{\pm}0.57g/ml$. There was no correlations between peak SUV and tumor volume. Two large malignant lesions ($> 1000 mm^3$) showed hot uptake on whole body scan. But two medium-sized lesions ($100-1000mm^3$) looked faint and two small ($<100mm^3$) lesions were not visualized. The images reconstructed with $256{\times}256$ matrix showed lesions more clearly than those with $128{\times}128$ matrix Conclusion: F-18-FDG PET scan is highly sensitivity in detecting malignant intraocular tumor For the evaluation of small-sized intraocular lesions, whole body scan is not appropriate because of low sensitivity. A regional scan with sufficient acquisition time is recommended for that purpose. Image reconstruction in matrix size of $256{\times}256$ produced clearer images than the ones in $128{\times}128$, but it does not affect the diagnostic sensitivity.