Technetium-99m-sestamibi scintigraphy compared with thallium-201 in evaluation of thyroid tumors

Technetium-gsm methoxyisobutylisonitrile (MIBI) is a myocardial perfusion imaging agent that has been reported to effectively localize in various tumors (e.g., lung and thyroid carcinomas and osteogenic sarcoma). To determine its usefulness in thyroid tumors, we compared Tc-99m-MIBI With Tl-201 imaging. Method: We evaluated 25 patients with thyroid tumors (papillary carcinoma in 11, follicular carcinoma in 2, follicular adenoma in 7, adenomatous goiter in 5). Fifteen metastatic lesions from differentiated thyroid carcinomas were also evaluated. Early (10 min after injection) and delayed images (120 min after injection) were obtained for both Tc-99m-MIBI and Tl-201 scintigraphy, Results: The early images showed very similar findings for both (TC)-T-99m-MIBI and Tl-201. However, the delayed images showed that malignant tumors tended to retain more tracer agent than benign nodules. Marked retention was in 61.5% (8 of 13) of Tl-201 images and 53.8% (7 of 13) of Tc-99m-MIBI images, For metastatic lesions from thyroid carcinomas, the findings for Tc-99m-MIBI imaging were nearly identical to those for Tl-201 imaging. A slight difference in clarity was seen that may have been due to the effect of the Tc-99m. Conclusion: Although Tc-99m-MIBI scintigraphy does not have particularly good results in differentiating malignant from benign thyroid tumors, it may be useful in evaluating metastases or predicting recurrence because of its better imaging characteristics.