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A sensitive technique for measuring thyroidal uptake of iodine-131.

1967; National Institutes of Health; Volume: 8; Issue: 2 Linguagem: Inglês

Henry N. Wellman, James G. Kereiakes, Thomas B. Yeager, Gerald J. Karches, Eugene L. Saenger,

Medical Imaging Techniques and Applications

In order to obtain quantitative estimates of pico-and nanocurie amounts of radioiodine in the thyroid, detection sensitivity can be increased by a combina tion of several techniques: namely, increasing detector size, decreasing back ground and reducing detector-to-thyroid distance to a minimum. The latter measure is potentially responsible for the greatest degree of increased sensi tivity, but requires stringent geometric considerations. Geometric correction can be achieved through the nearly proportional relationship of photopeak to Comp ton scatter ratio with thyroid depth. Use of such techniques to increase detec tion sensitivity is reported in this communication. In addition, data are given in tercomparing this unique system with a routine thyroid uptake system which has been previously calibrated with ORINS standards.5 Presently used routine thy roidal radioiodine uptake systems do not take full advantage of these techniques for increased detection sensitivity (1,2). An approach to increased detection sensi tivity has been reported by Eisenbud, et al (3,4). A shielded dual crystal system was employed in 1962 in an attempt to assess radioiodine in the thyroids of children as a result of environmental exposure (5). Further development of the dual crystal system, however, indicated a need not only to identify the presence of raclioiodine in the thyroid, but also to quantitate it. In 1964 Van Dilla et at (6) suggested either the use of the ratio of the more easily attenuated 30 keV x-ray of 131Iodine or the 27 keV x-ray of 125lodine to the 364 keY gamma ray of 131lodine as a means of assessing the depth of the thyroid within the neck. The concept for an appropriate means of thyroid depth correction is further developed by the technique herein employed, which utilizes the ratio of the 364 keV gamma of 131lodine to the Compton continuum in the energy spectrum.