Quantitative thyroid fluorescent scanning: technique and clinical experience

A method for quantifying thyroid gland iodine content using a modified fluorescence scanning system is described. The technique does not require a computer. Two single channel analyzers and digital scalers are used to determine net counts from iodine k-alpha x-rays and system response in counts per milligram is calibrated from studies of known quantities of iodine placed in thyroid phantoms. Fluorescence quantification of thyroid gland iodine content was performed in 250 patients with a wide variety of thyroid disorders. Thirty euthyroid patients judged to have no evidence of thyroid disease averaged 10.1 +/- 3.9 mg glandular iodine. Results for several major diagnostic categories were: untreated Graves' disease, 28 patients, 24.4 +/- 9.9 mg; diffuse euthyroid goiter, 14 patients, 16.1 +/- 7.4 mg; primary hypothyroidism, seven patients, 0.5 mg; and nontoxic multinodular goiter, 28 patients, 7.3 +/- 4.1 mg. Follow-up studies on patients treated for Graves' disease both medically and with 131I generally revealed elevated iodine contents in persistently hyperthyroid patients, lower than normal average amounts in euthyroid patients, and only trace amounts in hypothyroid patients. Although the clinical role of fluorescence iodine quantification remains to be fully established, the technique provides information not otherwise available on an important parameter of thyroid status.