THE USE OF TRACER DOSES OF RADIOACTIVE IODINE, I¹³¹, IN THE STUDY OF NORMAL AND DISORDERED THYROID FUNCTION IN MAN*†

Abstract

THIS report presents the results of a fact-finding survey concerning the uptake by the thyroid of tracer doses of radioactive iodine of mass 131, eight day half-life, during normal and disordered thyroid gland function in man. This type of study is made possible by the inability of the animal and human organisms to differentiate between the several isotopes of iodine. Thus the radioactive isotopes of iodine are concentrated in, and leave the thyroid gland, in the same manner as the stable form (1, 2). The natural disintegration of the radioactive material produces both gamma and beta rays (3). The beta rays are absorbed within 2 millimeters of tissue. The gamma rays pass through the skin and can be detected readily by a Geiger counter, thus providing a means of determining the presence of the isotope and its actual concentration, and serving as an indicator of the behavior of stable iodine within the body. The highly localized radiation delivered by the beta rays, and the lesser contribution of the gamma rays, have been taken advantage of for therapeutic purposes (4, 5, 6, 7). In the latter half of 1946, the United States Atomic Energy Commission released for investigative purposes, radioactive iodine of mass 131 (eight day half-life) from the atomic pile. The material became available to the authors in October 1946 and was used to assess its value in the therapy and diagnosis of toxic goiter. The latter part of the study was soon extended to a variety of clinical conditions in an attempt to evaluate the usefulness of this particular activity of the thyroid gland, iodine uptake, as an index of over-all thyroid function.