A Technique for Long-Term Measurements of Thyroid Function in Beagle Dogs Using Iodine 125

摘要

A procedure for measuring thyroid uptake and retention of I 125 is described. After a single dose of 1.85 MBq the thyroid retention curve can be followed for 3 to 6 months or more. Physiologic changes and experimental manipulations of thyroid function are observed by changes in the slope of the release curve. The form of the slope of the curve is useful for determining biological half life, evaluating changes in turnover, calculating release rate exponentials, and for analyzing iodine compartmental distribution. Backscatter and attenuation affect measurements of I 125 uptake more than measurements made with I 131. The major disadvantage of I 125 is the extent of its absorption in tissues, which is partially counterbalanced by backscatter from the tissues surrounding the thyroid. Backscatter in the Lucite neck phantom can exceed attenuation.