1. Department of Bioengineering and Cardiology Division, Department of Internal Medicine, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea, and Radiation Research Center for Industry and Environment, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 1266 Sinjeong-dong, Jeongeup-si, Jeollabuk-do, 580-185, Korea