A Scintillation Counter for Measurement of I 131 Uptake in the Thyroid Gland. ∗

Abstract

Summary

1. The problems inherent to the measurement of I¹³¹ uptake in the thyroid gland have been reviewed and the applicability of the scintillation counter for this use discussed. 2. The selection of scintillztion phosphor and construction of the counter has been described and compared in operation over a 6-weeks period with a conventional Geiger counter. This improvement of sensitivity has shown to be a factor of 30 ~ 50. 3. The increased sensitivity described has shown to be sufficient to allow an immediate reduction of the tracer dose from 100 μc to 50 μc, with a recent reduction to 25 μc. It may be seen that the dose could be reduced to 10 μc with considerable ease. At the same time a decided improvement over the Geiger counter in counting statistics has been obtained. Based on the previous counting rates the 10 μc standard would exhibit a counting rate ~ 2,700 c/m and an uptake rate ~ 1,200 c/m. Background for such measurements would be 200 ~ 400 c/m.