Continuous registration of the thyroidal uptake of sup(99m)Tc and 123I in the first 30 minutes

The continuous registration of the thyroidal uptake of intravenously administered sodium pertechnetate-sup(99m)Tc and sodium iodide-123I was performed in the same patients on consecutive days. Recording was for 30 min and a comparison was made of the uptake at 20 min and of the curves of thyroidal concentration of radioactivity during the 30-min period. In euthyroid patients the mean uptake +- standard deviation was 1.21 +- 0.66% for technetium and 2.48 +- 1.49% for iodine. This ratio of approximately 2.5, I/Tc, was obtained both for the euthyroid and hyperthyroid groups. However, individual patients showed a wide range of I/Tc ratios with seven patients having a ratio less than 1.0. Analysis of the shape of the curves was not helpful in that no consistent patterns were obtained associated with specific clinical conditions. It was concluded that the pertechnetate uptake is related to, but not a specific measure of, the iodide trap. (author)