Unexpected differences in early thyroidal trapping of iodide and pertechnetate

Compartmental analysis was applied to simultaneously acquired ¹³²I-iodide and ^99mTc-pertechnetate thyroid uptake data. The method allowed for arterio/venous differences in plasma tracer level and for an instantaneous phase of thyroid uptake.Observations in four thyrotoxic patients, before and during antithyroid drug therapy, revealed greater instantaneous uptake of TcO ₄ ^- . The results also revealed that instantaneous uptake of both I^– and TcO ₄ ^– may increase over the first six months of drug therapy. These findings could not be explained by the estimates of unidirectional clearance which were greater for I^- and varied little during the early stages of drug therapy.