99mTc Sestamibi Scans In Thyroglobulin Positive Scan Negative Differentiated Thyroid Cancer (DTC) Patients

This study is being done to see if the radioisotope 99mTc sestamibi scans can locate what is causing the elevated serum thyroglobulin in persons with differentiated thyroid cancer who have elevated serum thyroglobulin levels and negative diagnostic imaging tests. This is for patients with: * Elevated suppressed or stimulated thyroglobulin level (Tg) \> 10 ng/ml with or WITHOUT thyroglobulin antibodies , * All NEGATIVE standard diagnostic clinical imaging studies (NSDCIS), which includes all the following negative studies: ultrasound (US), diagnostic radioiodine scan (DRS), chest-x-ray (CXR), computer tomography with or without contrast (CT), and 18F-Fluoro-deoxyglucose positron emission computer tomography scan (18F-FDG PET) within the last 12 mos. * If NSDCIS and negative brain CT or magnetic resonance (MR) are performed and are negative, voluntary patients will have 99mTc sestamibi scan performed in 4 phases: Phase 1: receive an injection into their vein of a radioisotope called 99mTc sestamibi. Phase 2: wait for 60 to 90 minutes in a waiting room Phase 3: imaged lying face up on an imaging table while a camera passes around you from the top of the head to approximately the level of knees. This requires approximately 45 minutes Phase 4: images will be reviewed by the nuclear medicine physician. This will take \~10-15 minutes. If additional images are required to clarify an image, then additional images of that area will be performed on the same camera or an alternate camera. As earlier, the additional images performed lying face up. These images require \~20-45 minutes. The patient will then be released. Interpretation of 99mTc sestamibi Study. A. A team of two blinded nuclear medicine physicians will interpret the 99mTc sestamibi, and any area of radioactivity will be graded as by a standard nuclear medicine grading system: 1. Normal physiological activity 2. Probably physiological activity 3. Indeterminate activity 4. Probably metastatic disease 5. Metastatic disease B. Criteria for "final determination" regarding whether a finding represents physiological activity or metastatic disease: 1. For findings graded as 1 or 2, they will be defined for this study as physiological activity. 2. For findings graded as 3, or 4, the following will be required: i. Biopsy; however, this will only performed if clinically indicated. 1\. Follow-up: It is anticipated that very few biopsies will be performed and because the criteria for entering this study is NDCIS., the only alternative for confirming whether or not a foci of 99mTc sestamibi uptake on a scan is metastases will be follow up, which will be performed on a clinical basis. However, if on follow up any of the following occur, then the focus will be categorized as a metastases (true positive). 1. Subsequent biopsy, 2. Subsequent clinical imaging study(s) (For example, although a lytic bone lesion in the area of interested was not present initially on the CT, a lytic lesion indicative of metastases may subsequently develop in that area, and for this study this will be defined as evidence of metastases of DTC (true positive). ii. Blind I-131 treatment\*\* with or without a prefatory scan: If a "blind" I-131 treatment" is clinically selected and the post I-131 therapy scan demonstrates uptake in the same areas as the 99mTc sestamibi, then the finding on the 99mTc sestamibi will be classified for this study as a metastases of DTC. 3. Grade 5 is not anticipated, because unlikely I-131, which can have patterns that are very specific for DTC, 99mTc sestamibi patterns are not specific for DTC. * A "blind I-131 treatment" is a potential therapeutic option, and this term means that the treating physician or team cannot identify the source of the patient's elevated Tg, but because of factors such as the level of elevated Tg, the rate of rise of the Tg, and the patient's clinical situation, a therapeutic administration of I-131 is give despite being "blind" to the source of the Tg.