EARLY AND DELAYED TL-201 SCINTIGRAPHY IN THYROID-NODULES - THE RELATIONSHIP BETWEEN EARLY TL-201 UPTAKE AND PERFUSION

Seventy-six patients with thyroid nodules were studied. Initially, 74 MBq of thallium-201 was injected. The thyroid gland was imaged 15 min (early) and 3 h (delayed) after the injection. Thereafter, 185 MBq tec hnetium-99m pertechnetate was injected. Immediately after the injectio n, a 1-min perfusion image was acquired, followed by an image at 20 mi n. Increased early and delayed Tl-201 uptake compared with the contral ateral thyroid tissue was adopted as the criterion for malignancy. Sen sitivity, specificity and negative predictive values were found to be 85%, 64% and 78%, respectively, in operated patients, but these values were 86%, 87% and 95 %, respectively, in the whole group, including p atients followed with fine-needle aspiration biopsy. With the purpose of investigating the relationship between perfusion and early Tl-201 u ptake, both perfusion and early images were graded comparing nodular a ctivity with contralateral thyroid activity. There was a poor correlat ion between perfusion and Tl-201 uptake. The correlation was even wors e in hyperactive nodules. It is concluded that early and delayed Tl-20 1 imaging should not be used in the differential diagnosis of cold nod ules and that early Tl-201 uptake seems to be more closely related to factors other than perfusion.