• Progress in Medical Physics
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• v.11 no.1
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• pp.59-71
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• 2000

It is possible to obtain a fast CT scan during breath holding with spiral technique. But the risk of radiation is increased due to detailed and repeated scans. However, the limitation of X-ray doses is not fully specified on CT, yet. Therefore, the purpose of the present study is to define the limitation of X-ray doses on CT The CT unit was somatom plus 4. Alderson Rando phantom, Solenoid water phantom, TLD, and reader were used. For determining adequate position and size of organs, the measurement of distance(${\pm}$2mm) from the midline of vertebral body was performed in 40 women(20~40 years). On the brain scan for 8:8(8mm slice thickness, 8mm/sec movement velocity of the table) and 10:10(10mm slice thickness, 10mm/sec movement velocity of the table) methods, the absorption doses of exposed area of the 10:10 were slightly higher than those of 8:8. The doses of unexposed uterus were negligible on the brain scan for both 8:8 and 10:10. On the chest scan for 8:8, 8:10(8mm slice thickness, 10mm/sec movement velocity of the table), 10:10, 10:12(10mm slice thickness, 12mm/sec movement velocity of the table) and 10:15(10mm slice thickness, 15mm/sec movement velocity of the table) methods, 8:8 method of the absorption doses of exposure area was the most highest and 10:15 method was the most lowest. The absorption doses of 8:10 method was relatively lower than those of the other methods. In conclusion, the 8:10 method is the most suitable to give a low radiation burden to patient without distorting image quality.

• Korean Journal of Ecology and Environment
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• v.55 no.3
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• pp.231-243
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• 2022

Anthropogenic disturbances on freshwater ecosystem are known to degrade biodiversity, especially on fish assemblage. In this study, we have conducted fish surveys to identify impact of a bridge construction on fish assemblages. A total of eight study sites were surveyed in the Danjang and the Dong Stream in southern part of South Korea from June to November in 2021. The fish samplings were carried out five times, using cast-nets(10×10 mm mesh size), scoop-nets(4×4 mm, 5×5 mm mesh size), set-nets (10×10 mm mesh size), and fish traps (3×3 mm mesh size), along with the Stream/River Ecosystem Survey and Health Assessment by the Ministry of Environment of Korea and basic water quality measurement. Also, we applied the species diversity index and length-weight relationship regressions on certain species to identify interspecific growth rate differences in accordance with study sites. As a result, a total of 782 individuals, 23 species and 10 families were collected. The dominant species was Zacco Koreanus and relative abundance was 50.89%. When applying the length-weight relationship regressions on certain species, the 'b' value for Z. Koreanus was lower at the downstream points than at the upstream points of the construction site. In addition, when comparing to the results of the past survey, relative density of demersal fish at the upstream and downstream points decreased from 26% to 1.4%, and from 18% to 6.3%, respectively. In conclusion, it is considered that bridge construction negatively affects the habitat of fishes, especially on demersal fishes. Therefore, appropriate conservation efforts such as installation of silt protector and sand sedimentation pond are needed to alleviate the disturbance in habitat such as occurrence of turbidity and destruction of micro-habitats.