Radioimmunoscintigraphy using iodine-131-anti-CEA monoclonal antibodies and thallium-201 scintigraphy in medullary thyroid carcinoma: a case report. This case report demonstrates the use of thallium-201 (201Tl) scans versus iodine-131- (131l) anti-CEA F(ab')2 scans in a patient with high serum CEA levels due to metastases of medullary thyroid carcinoma in the suprarenal region and sacroiliacal region. Scintigraphy using monoclonal antibodies directed against CEA showed a higher tumor uptake (0.26% dose and 0.64% dose, respectively) than a thallium scan and is believed to be promising for future radiotherapeutic applications. 