Thyroidal Uptake and Turnover of the Pertechnetate Ion in Normal and Hyperthyroid Subjects

The thyroid uptake and plasma activity of 99mTc have been followed for times up to 6 hr after intravenous administration of 1 me of 99mTc. The 20-min thyroid uptake of pertechnetate was found to discriminate between euthyroid and hyperthyroid subjects. When the plasma clearance of pertechnetate was calculated in the same way as the plasma clearance of radioiodide, this clearance was found to decrease rapidly with time due to return of pertechnetate from the intrathyroidal pool. An attempt to analyze the kinetic data on the basis of a 2-compartment model was successful, suggesting that no significant quantities of pertechnetate are organically bound in the thyroid. From this analysis the unidirectional clearance, the intrathyroidal turnover rate and the intrathyroidal space were calculated. Both the unidirectional clearance and the intrathyroidal space were markedly different in euthyroid and hyperthyroid subjects. The intrathyroidal turnover rate, however, was similar in euthyroid and hyperthyroid subjects.