18F-FDG uptake in malignant cells is mainly due to the increase of glucose transporter (especially GluT-1) in cell membrane and hexokinase such as HK-II.. Due to the decreasing of natri / iodine symmporter (NIS) and increase of glucose transpoter (GLUT) in cell membrane, 18F-FDG PET / CT plays an important role in diagnosis of recurrence, 4 metastasis and change of treatment strategy in postsurgica l DTC with high serum Tg and negative 131I WBS.