FDG PET imaging was performed 32 cases of papillary (n = 18 ) and follicular ( n = 14 ) thyroid carcinoma after thyroidectomy. In order to evaluate the influence of serum TSH level on results of 18FDG PET imaging

the patients were divided into two groups with under TSH suppression ( TSH≤0.3μIU/mL ) and without TSH suppression ( TSH > 0.3 μIU/mL )

respectively. The uptake levels of FDG in recurrent or metastatic lesions in 18 two groups were compared by SUV and the tumor-to-background ratios ( TBRs ) . Fourteen of 32 patients had positive FDG PET imaging with 6 and 8 patients in under TSH suppression group and without TSH suppression 18 group

respectively. The difference between two groups didn’t reached significance ( χ2 = 1.814

P = 0.178 ) . 3 recurrent patients within under TSH suppression group and proved by clinical follow up had false negative of FDG 18 PET imaging. Total 24 metastatic lesions were found and analysed by SUV and TRBs. The uptake level of FDG in 18 lesions of without TSH suppression group was higher than under TSH suppression group. Statistical study showed that the difference between two groups has reached significant level ( P < 0.05 ) . This study demonstrated that serum TSH level could influence the uptake of FDG in recurrent or metastatic lesions of differentiated thyroid carcinoma. 18