Twenty-four hours following the administration of Thyrogen or the modified release formulation, a subset of five (5) subjects in each treatment arm will receive a dose of 123I prepared to be 400µCi on the day of radioiodine administration based on the utilized nuclear pharmacy's calibration schedule. Thyroid gland uptake will be measured via a probe in these 10 subjects at 6, 24 and 48 hours following radioiodine administration.