Comparison of Iodine-124 (I-124) and Iodine-131 (I-131) Radiopharmacokinetics in Patients Prepared With Recombinant Human TSH Injection (rhTSH)

"After TSH stimulation with Recombinant human TSH (rhTSH) for 2 days, a dose of radioactive iodine 124 ( I-124) 1.7 mCi is administrated orally and PET imaging is done for 5 continuous days including the day of the dose administration. On each day, just before imaging, 5 ml of blood is drawn.~Patients will be randomized to either the sequence above (e.g. I-131 followed by I-124) or to the reverse sequence in which the I-124 is given first followed by the I-131. If I-124 is administered first and as long as the whole body retention is \< 2% by the start of the second rhTSH stimulation, the I-124 will not interfere with the I-131."