jung-su kim department of radiologic science, college of health science, korea university, seoul, south korea sang-wook yoon department of diagnostic radiology, cha bundang medical center, cha university, gyeonggi-do, south korea deok-nam seo department of radiologic science, college of health science, korea university, seoul, south korea so-ra nam department of radiologic science, college of health science, korea university, seoul, south korea jung-min kim department of radiologic science, college of health science, korea university, seoul, south korea; department of radiologic science, college of health science, korea university, seoul, south korea. tel: +82-2940-2577, fax: +82-29402829