201Tl in the scintigraphic evaluation of the "cold" thyroid areas

201Tl-chloride, which has a metabolic behaviour similar to that of potassium and cesium, has been used in 68 patients for the evaluation of thyroid nodules previously recognized as "cold" on 131I or 99mTc scans. All patients were re-examined with gamma-camera and/or sequential scintigraphic recordings during 60 min after i.v. administration of thallium. In some cases, simultaneous imaging and integral digital plot with 131I or 99mTc and 201Tl were performed. In all 12 malignant nodules, 201 Tl has showed a high uptake, while it did not concentrate in 47 benign nodules (cystic or macrofollicular adenomas); thallium uptake was nevertheless found in 10 solid neoformations in which histological pictures were negative for malignancy or atypical lesions. The computerized study of the 201Tl intranodular concentration, with the analysis of its dynamic function curves, seems to offer further possibility in differentiating and in a more objective evaluation of the "cold" areas on the thyroid scan.