Value of (18)F-FDG Hybrid PET/MR in Differentiated Thyroid Cancer Patients with Negative (131)I Whole-Body Scan and Elevated Thyroglobulin Levels

PURPOSE: To evaluate the diagnostic performance of (18)F-FDG PET/MR in detecting recurrent or metastatic disease in patients with differentiated thyroid cancer (DTC) who have increased thyroglobulin (Tg) levels but a negative (131)I whole-body scan (WBS). The relationship between (18)F-FDG PET/MR and serum Tg levels was explored. We also evaluated the therapeutic impact of PET/MR on patient clinical management. PATIENTS AND METHODS: Twenty-nine DTC patients with a negative (131)I-WBS of the last post-therapeutic and increased Tg levels under thyroid-stimulating hormone suppression treatment who underwent (18)F-FDG PET/MR examination were retrospectively analyzed. RESULTS: Of those 29 patients, (18)F-FDG PET/MR findings were true positive, true negative, false positive, and false negative in 18, 7, 2, and 2 patients, respectively. The overall sensitivity, specificity, and accuracy were 90.0%, 77.8%, and 86.2%, respectively. We noticed significant differences in serum Tg levels between the PET/MR-positive and PET/MR-negative patient groups (P=0.049). Receiver operating characteristic curve analysis showed that a Tg level of 2.4 ng/mL was the optimal cut-off value for predicting PET/MR results. The sensitivity, specificity, and accuracy of PET/MR were higher in patients with Tg levels greater than 2.4 ng/mL than in patients with lower levels. By detecting recurrent or metastatic disease, (18)F-FDG PET/MR altered the clinical management in 7 patients (24.1%) of the overall population. CONCLUSION: (18)F-FDG PET/MR has high diagnostic accuracy for detecting recurrent or metastatic diseases in DTC patients and is useful for clinical management.