Radionuclide thyroid scans

Sodium pertechnetate Tc-99m was introduced for scanning the thyroid (Harper 1964) and for brain scanning (McAfee et al. 1964 Quinn 1965), primarily because of its physical properties other applications followed (Harper et al. 1966). The striking similarity of the heptavalent anion with iodide, however, has made pertechnetate an excellent radionuclide for thyroid scanning and for the study of thyroid physiology (Andros et al. 1965 Kusic et al. 1990). 

Although iodine has several radioactive isotopes, greatest use has been made of I. It has a half-life of 8 days therefore, more than 99% of its radiation is expended within 56 days. Its radioactive emissions include both y rays P and particles. The short-lived radionuclide of iodine, I, is primarily a y-emitter with a half-life of only 13 hours. This permits a relatively brief exposure to radiation during thyroid scans. 

Pretherapeutic evaluation of the thyrolaryngeal tumors should include conventional radiograms, CT, ultrasound and radionuclide scanning. The highly vascularized tumors of this region are usually supplied by the superior and inferior thyroidal arteries and are the most likely involved in the endovascular treatment. These arteries are usually widely selected for endovascular embolization of other head and neck tumors due to the collateral supply to the floor of the mouth and the carotid region. 

Brill AB, Patton JA, Hollifield J. 1974. Thyroid fluorescent scanning. In Proceedings of a symposium on thyroid and endocrine system investigations with radionuclides. Miami. Chap. 6. 

The in-vivo technique has been used to investigate patients with normal and pathological thyroids referred to the Nuclear Medicine Department for routine radionuclide scanning. The study was approved by the Guy s Hospital Medical School Ethical Committee and informed consent was obtained from each patient prior to the fluorescent examination. In each case, iodine measurement was carried out before any radionuclide was administered to the patient for the routine scan. 

The investigation of children with thyroglossal cysts shows a definite useful clinical application of the fluorescent technique using either a scanner or a stationary system. These cysts may be confused with ectopic thyroids and misdiagnosis may lead to excision of the patient s only thyroid tissue and result in hypothyroidism. It is thus essential to establish that a normal thyroid is present before excising a suspected thyroglossal cyst. A radionuclide scan is usually advised but a fluorescent study either with a scanner or more simply with a... 

We conclude that solitary thyroid nodules that are cold on radionuclide scan, solid on ultrasound examination and devoid of iodine on XEF study should be excised as they carry the highest risk of malignancy. 

Barbato A.L., Bekerman C., Refetoff S. 1977 Transient iodide trapping defect in Hashimoto s thyroiditis detected by the combination of radionuclide and fluorescent scanning. Br.J.Radiol. 50 827-830. 

---