Scintigraphic evaluation of functional thyroidal autonomy

The scintigraphic evaluation of thyroidal autonomy is performed both as a q uantitative and qualitative thyroid scintigraphy with 99m-Tc-pertechnetate (99m-TcO4-), using a gamma camera fitted with an on-line computer system. A strong and linear correlation between the global 99m-Tc-pertechnetate thyr oid uptake (TCTU) and I-123 clearance has been recognised. Therefore TCTU-v alues can be used as an reliable equivalent of the iodine clearance in the evaluation of actual thyroid function. The clinical value of the TCTU in th e diagnosis of thyroidal autonomy is limited because it represents iodine c learance of both normal and autonomous tissue. As a consequence scintigraph ic diagnosis and quantification of autonomy can only be established if the global 99m-Tc-pertechnetate thyroid uptake under suppression (TCTUs) is det ermined. This method is valuable in risk stratification of spontaneous or i odine induced hyperthyroidism, in the estimation of the target volume prior to radioiodine therapy and in the evaluation of therapeutic success after definitive therapy.