Brown Adipose Tissue Activity and Thyroid Hormone

Rationale: During the last decades, research in possible therapies for existing obesity and developmental factors causing obesity has explosively increased. Recently renewed interest aroused for a tissue playing a possible role in both development and therapy for obesity: brown adipose tissue (BAT). To define the relation between BAT and thyroid hormone, the investigators set up the following research protocol. In this protocol BAT activity will be determined in subjects that underwent thyroidectomy for well-differentiated thyroid carcinoma. Objective: To study the effect of thyroid hormone and thyroid-stimulating hormone on brown adipose tissue activity. Study design: Determine BAT activity after thyroidectomy in well-differentiated thyroid carcinoma patients. Study population: Patients that underwent thyroidectomy for well-differentiated thyroid carcinoma, male and female, aged 18-65 years. Intervention: FDG-PET-CT-imaging (\[18F\]fluorodeoxyglucose positron-emission-tomography computed-tomography) of BAT activity will be performed under cold stimulation twice. For patients clinically withdrawn from thyroid hormone suppletion, the first occasion will be in a hypothyroid state within 4-6 weeks after thyroidectomy and the second measurement will take place in a euthyroid state 4 months after the start of thyroid hormone treatment. For patients receiving recombinant-thyroid-stimulating-hormone injections, the first occasion will be shortly after the injection in a state of high thyroid-stimulating hormone levels. The second measurement will be in a euthyroid state 4 months after the injection. Main study parameters/endpoints: The main endpoint of this study is the effect of thyroid hormone and thyroid-stimulating hormone on BAT activity in kBq (kilobecquerel) and SUV (standard uptake value). Secondary endpoints are the effects of thyroid hormone and thyroid-stimulating hormone on energy metabolism, body core temperature, skin surface temperatures and skin per