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) = negative 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 EDCIS (extensive diagnostic clinical imaging studies of 18F-sodium fluoride positron emission computer tomography scan (18F NaF PET) or 99mTc methylene diphosphonate bone scan (99mTc MDP), AND negative brain CT or magnetic resonance (MR) are performed, these are also negative. Voluntary patients will have 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. The risk of this study is considered very low, and the potential benefits to the patient are considered very high.