A comparative study of 99mTc and 131I in thyroid scanning.

Thyroid scans performed with both 99mTc pertechnetate (99mTcO4) and (131I) were compared in 46 patients with palpable thyroid nodules to determine whether 131I scanning is any longer a necessary procedure. A discrepancy between the two types of scan existed in only three cases, in one of which the thyroid nodule showed uptake of 99mTcO4 but not of 131I. Subsequent surgery revealed a thyroid malignancy in this patient. In each of the other two discrepancies a nodule "cold" on 99mTcO4 scanning was apparently functioning on 131I scanning, and was found to be benign at surgery. As the convenience and lower radiation absorbed dose of 99mTcO4 patients compared with 131I make it a better scanning agent, it is recommended that 99mTcO4 scans of the thyroid be first nodules. If these nodules prove to be functioning equally with paranodular tissue, a 131I scan should also be performed to help exclude a possible thyroid malignancy.