The use of technetium-99m pertechnetate in postoperative thyroid carcinoma. A comparative study with iodine-131.

Over 3 years, a prospective comparison was made between Tc-99m pertechnetate and I-131 for the detection of residual and metastatic tissue in the follow-up of patients with cancer of the thyroid. All patients stopped thyroid medication for a minimum of 4 weeks. All patients had imaging done first with Tc-99m pertechnetate followed within a maximum of 2 weeks by I-131. The study included 66 patients in whom 81 studies were done with both Tc-99m and I-131. The results showed that 27 studies were positive with both Tc-99m and I-131 (true positive): 19 in the thyroid bed, four lymph nodes, two bony metastases, and two pulmonary metastases. Five patients had negative results with Tc-99m and positive results with I-131 (false negative): three in the thyroid bed, one lymph node metastasis, and one pulmonary metastasis. Only one case was positive with Tc-99m in the neck but negative with I-131 (false positive). The remaining 48 studies were negative both with Tc-99m and I-131 (true negative). Considering I-131 imaging as the standard procedure, Tc-99m had a sensitivity of 87%, specificity of 97%, and accuracy of 92.5% for the detection of residual or metastatic functioning thyroid tissue.