Inclusion Criteria:

- Adults (aged ≥ 18 years) with history of treated well-differentiated epithelial
thyroid carcinoma (papillary, follicular or Hurthle cell), for which total or near
total thyroidectomy plus postoperative radioiodine remnant ablation with 131-I has
either been performed or found to be unnecessary by radioiodine imaging after TSH
stimulation.

- Serum thyroglobulin (Tg) concentration ≥ 10 ng/mL (in the absence of interfering Tg
autoantibodies).

- No findings of a "qualifying" radioiodine whole body scan that are sufficient to
localize the disease suspected on the basis of the serum Tg.

- Inconclusive disease localization despite clinical assessment, cervical sonography,
CT or magnetic resonance (MR) of the chest, and when appropriate other imaging and
biopsy procedures. Patients must have no more than three foci of known or suspected
extra-cervical metastasis.

- Must be in stable medical condition.

- Must be able to fully understand the protocol and be compliant with instructions.

Exclusion Criteria:

- Diabetes mellitus, due to interference with fluorodeoxyglucose (FDG) PET scanning.

- Claustrophobia, inability to lay supine, or other factors preventing cooperation with
scanning procedures.

- Withdrawal of thyroid hormone or rTSH administration within the preceding month.

- Presence of circulating Tg autoantibodies interfering with serum Tg measurement.

- Women who are pregnant or breastfeeding