(18)F-FDG PET/CT for the Preoperative Diagnosis of Papillary Thyroid Microcarcinoma: The Value of Dual Time Point Imaging

Seo, Young Duk; Kim, Seong Min; Kim, Kun Ho; Kim, Je Ryong

Abstract

PURPOSE
We studied the patterns of FDG uptake of primary papillary thyroid microcarcinoma (PTMCa) lesions and benign thyroid nodules in dual time point (18)F-FDG PET/CT imaging.
MATERIALS AND METHODS
Consecutive 134 patients (154 lesions) with PTMCa and 49 patients (61 nodules) with benign thyroid nodules equal to or less than 1.0 cm who underwent dual time point (18)F-FDG PET/CT study before surgery were enrolled. We calculated the maximum standardized uptake value of PTMCa and benign nodules in both time points, and percent change of SUVmax (delta%SUVmax) and lesion to background ratio of SUVmax (delta%L:B ratio) between both time points. The mean time interval between scans was 23.4+/-4.4 minutes (thyroid to thyroid interval: 10.7+/-4.4 minutes).
RESULTS
The mean of SUVmax of PTMCa was increased from 4.9+/-4.3 to 5.3+/-4.7 (p<0.001) and delta%SUVmax was 12.3+/-23.6%. But, the mean of SUVmax of benign nodules was no definite change (2.1+/-1.0 to 2.1+/-1.3, p=0.686) and delta%SUVmax was -0.3+/-20.5%. Of the 154 PTMCa, 100 nodules (64.9%) showed an increase in SUVmax over time, while 19 (31.1%) of the 61 benign thyroid nodules showed an increase (p<0.001). The dual time point (18)F-FDG PET/CT found more PTMCa in visual assessment (62.3% vs. 76.6%, p=0.006), even in smaller than 0.5 cm (38.6% vs. 60.0%, p=0.011).
CONCLUSION
Dual time time (18)F-FDG PET/CT imaging was more useful than single time point (18)F-FDG PET/CT imaging for distinction between PTMCa and benign nodule, especially when nodule showed equivocal or negative findings in single time point (18)F-FDG PET/CT imaging or was smaller than 0.5 cm.