THE DIRECT MEASUREMENT OF I¹³¹UPTAKE IN THE THYROID GLAND; FURTHER OBSERVATIONS*

Abstract

ALTHOUGH the usefulness of radioactive iodine (I131) in the study of thyroid gland function and in the treatment of hyperthyroidism is well established, many problems exist in the absence of a satisfactory method for accurate direct measurement of I131 in the thyroid gland in situ. Many previous studies (1–8) have utilized urinary I131 excretion. Although the urinary I131 content can be accurately measured, the urinary I131 excretion is, at best, an indirect indicator of thyroid gland function. In edematous and in uncooperative patients considerable error may be encountered. In other studies (9–16) direct measurements have been made by external counting over the thyroid gland with a single Geiger-Mueller tube. This method demands highly accurate positioning of the patient. Errors due to variation in gland size and location (geometry, absorption and scatter) are large and methods for their correction are not satisfactory (17, 18) for general clinical use. In addition, with the data gathered by the above methods, various attempts have been made to solve the problem of thyroid gland uptake of radioactive iodine by mathematical analyses (19–21). The need remains, however, for a direct, simple, quantitative method for measurement of I131 uptake by the thyroid gland.