An efficient technique for the reproducible in vivo assay of thyroidal radioiodine in small animals

Abstract

In in vivo thyroid radioiodine assay with a single detector, unavoidable variation in the position of the animal produces significant error unless the source to detector distance is great. In this paper, a system is described in which the sacrifice of efficiency for precision is avoided through the use of two opposed detectors that yield highly reproducible count rates despite uncertainty in the exact position of the source. This geometry independence permits precise, automated counting of unanaesthetized and relatively unrestrained rats. Excised organs and standards can be assayed in the apparatus, allowing accurate determination of isotope uptake. Iso-response curves and data on precision, specificity, sensitivity and accuracy are given. With appropriate modification, the twin-opposed detector design can be applied to a variety of in vivo counting problems.