 This project aims to evaluate the effects of the different stimulation, endogenous and exogenous, over renal function by glomerular filtration rate determined by 51Cr-EDTA. This will be a controlled and randomized study in which 44 patients that has clinical indication of remnant ablative radioiodine treatment will be prepared by either one of the TSH stimulation procedures. Additionally radiation dosimetry calculus will be done to analyze the levels of the patients radiation exposure associated with each of the uptake stimulation procedures for radioiodine therapy. 