Kinetics of 201Tl uptake in adenomas and well-differentiated carcinomas of the thyroid. A double isotope investigation with 99Tcm and 201Tl.

A visually increased uptake of 201Tl chloride corresponding to a 'cold' (131I or 99Tcm ) thyroid nodule is mostly seen in well-differentiated carcinomas but also often in follicular adenomas. Since a visually increased uptake of 201Tl can be due to an increased initial uptake and/or a delayed elimination, an extended dynamic investigation was performed in patients with well-differentiated carcinomas or with follicular adenomas. Data were collected in a dynamic simultaneous double isotope ( 99Tcm + 201Tl) study up to 50 min after intravenous administration. Adenomas could be significantly separated from carcinomas by the elimination (p = 0.0001), but not by the initial uptake.