The objective of this study is to compare the activity of radioiodine (131I) in patients taking Thyrogen with normal thyroid activity versus patients with hypothyroid activity after thyroid replacement medication is withdrawn. In addition the study will provide information on how radioactive iodine is eliminated from the body. The study will help researchers understand how to give Thyrogen and radioiodine for purposes of scanning and therapeutic ablation (the destruction of function) of cancerous thyroid tissue.