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Tl-201 thyroid imaging in differentiating benign from malignant thyroid nodules.

To evaluate the value of Tl-201 thyroid imaging in differentiating benign from malignant thyroid nodules, 58 patients with histologically proven thyroid masses were studied. The nature of the thyroid tumor was initially assessed by Tc-99m scans. Early and delayed Tl-201 thyroid imaging were performed in all patients, and thallium uptake and clearance in the cold nodules were assessed visually. Of the 20 patients with histologically proven malignant nodules, 19 showed increased Tl-201 activity in both the early and delayed images, indicating a sensitivity of 95%. On the other hand, 35 out of the 38 patients with benign nodules showed no increased thallium activity in the nodules on the delayed images, indicating a specificity of 92%. When early thallium images were analyzed separately, the sensitivity was 100% but the specificity was only 37%. By combining early and delayed Tl-201 images, differentiation between benign and malignant cold nodules is feasible. False-positive and false-negative cases will be discussed.