• Economic and Environmental Geology
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• v.31 no.3
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• pp.185-199
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• 1998

Hydrogeochemical and environmental isotope studies were undertaken for various kinds of water samples collected in 1995-1996 from the Bugok geothermal area. Physicochemical data indicate the occurrence of three distinct groups of natural water: Group I ($Na-S0_4$ type water with high temperatures up to $77^{\circ}C$, occurring from the central part of the geothermal area), Group II (warm $Na-HCO_{3}-SO_{4}$ type water, occurring from peripheral sites), Group III ($Ca-HCO_3$ type water, occurring as surface waters and/or shallow cold groundwaters). The Group I waters are further divided into two SUbtypes: Subgroup Ia and Subgroup lb. The general order of increasing degrees of hydrogeochemical evolution (due to the degrees of water-rock interaction) is: Group III$\rightarrow$Group II$\rightarrow$Group I. The Group II and III waters show smaller degrees of interaction with rocks (largely calcite and Na-plagioclase), whereas the Group I waters record the stronger interaction with plagioclase, K-feldspar, mica, chlorite and pyrite. The concentration and sulfur isotope composition of dissolved sulfate appear as a key parameter to understand the origin and evolution of geothermal waters. The sulfate was derived not only from oxidation of sedimentary pyrites in surrounding rocks (especially for the Subgroup Ib waters) but also from magmatic hydrothermal pyrites occurring in restricted fracture channels which extend down to a deep geothermal reservoir (typically for the Subgroup Ia waters). It is shown that the applicability of alkaliion geothermometer calculations for these waters is hampered by several processes (especially the mixing with Mg-rich near-surface waters) that modify the chemical composition. However, the multi-component mineral/water equilibria calculation and available fluid inclusion data indicate that geothermal waters of the Bugok area reach temperatures around $125^{\circ}C$ at deep geothermal reservoir (possibly a cooling pluton). Environmental isotope data (oxygen-18, deuterium and tritium) indicate the origin of all groups of waters from diverse meteoric waters. The Subgroup Ia waters are typically lower in O-H isotope values and tritium content, indicating their derivation from distinct meteoric waters. Combined with tritium isotope data, the Subgroup Ia waters likely represent the older (at least 45 years old) meteoric waters circuated down to the deep geothermal reservoir and record the lesser degrees of mixing with near-surface waters. We propose a model for the genesis and evolution of sulfate-rich geothermal waters.

• Journal of the Korean Society of Radiology
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• v.81 no.4
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• pp.899-911
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• 2020

Purpose To evaluate the safety and efficacy of the newly designed open-cell type self-expandable nitinol stent (NiTi-stent) for peripheral arteries. Materials and Methods Twenty-eight limbs of 14 minipigs were randomly assigned to the NiTistent group or conventional nitinol stent group. Stents were symmetrically implanted into the iliac arteries of each animal using carotid artery approach and were observed for 1 month (n = 5) and 6 months (n = 9). The angiographic lumen diameter (ALD), late lumen loss, angiographic stenosis, histomorphometric lumen area, neointimal area, and area stenosis were analyzed and compared between the groups. Results Stent migration, stent fracture, or thrombus formation were not observed in either group. At the 1-month follow-up, the neointimal area (p = 0.008) and area stenosis (p = 0.016) were significantly smaller in the NiTi-stent group than in the control group. At the 6-months followup, the NiTi-stent group showed significantly larger ALD (p = 0.014), less late lumen loss (p = 0.019), less angiographic stenosis (p = 0.014), larger lumen area (p = 0.040), and smaller neointimal area and area stenosis (p = 0.004 and p = 0.014, respectively) compared with the control group. Conclusion The NiTi-stent is as safe and effective as the conventional nitinol stent and induces less neointimal hyperplasia in a minipig iliac artery model.