Brown adipose tissue (BAT) is important in energy expenditure through thermogenesis although the regulatory factors are not well known in humans. There is evidence suggesting that the thyroid hormones affect BAT functions in lower mammals, but the effects of the thyroid hormones on BAT activity in humans are still unclear. The objective of this study was to investigate the effects of thyroid hormones on glucose metabolism of BAT and other organs in humans.

Twenty consecutive patients with Graves'-caused hyperthyroidism who are newly diagnosed and untreated will be studied at the Endocrine Department of Huashan Hospital, Fudan University. All subjects are screened and examined by two senior investigators. Putative BAT activity is determined by the integrated 18F-fluorodeoxyglucose (18F-FDG) PET-CT. After the first PET scan, hyperthyroid patients will be treated with Methimazole following clinical guidelines. None of them uses beta adrenergic blockade. The initial dose of methimazole employed is 10mg thrice a day. During follow-up, the thyroid hormone levels (free triiodothyronine and free thyroxine) will be measured every twenty days. The PET-CT scans and assessments will be repeated when the symptoms have disappeared and the thyroid hormone levels return to normal range. Then the dose of methimazole will be adjusted accordingly.

Inclusion Criteria:

• Newly diagnosed and untreated hyperthyroid patients
• Informed consent was obtained

Exclusion Criteria:

• History of other endocrine diseases
• Useing beta adrenergic blockade
• Pregnant women
• Pacemaker implantation

Twenty Graves' disease-caused hyperthyroid patients who were newly diagnosed and untreated were included. All hyperthyroid patients were treated with Methimazole and had been followed up until their symptoms disappeared and the thyroid hormone levels went back to normal range.