Radioisotope X-ray fluorescence technique in the dynamic study of thyroid behaviour under iodine load

Abstract

A presentation is made of equipment based on the principle of excitation of X fluorescence by means of radioisotope sources. The technique has been used to study the evolution of stable iodine concentration (¹²⁷I) in the human thyroid in vivo with a minimum variation in weight of ∼50 parts per million.

The equipment is characterized by the use of 2 collimated sources of ²⁴¹Am, each of 45 mCi, and by a proportional gas counter. The measuring times required are of approximately 100 sec each. The dose absorbed for each measurement is less than 30mrem at the level of the neck surface and less than 1 mrem at the thyroid.

Preliminary tests have been carried out over one month in an apparently normal subject given increasing doses (6–30 mg) of stable iodine.

Curves of the spatial distribution and of the temporal evolution of the counts due to the radiation of X_k fluorescence emitted from the stable iodine atoms present in the thyroid were obtained in a preestablished constant area of the thyroid.

Since, under constant geometrical conditions, these counts are proportional to the concentration of iodine the pattern of the curve enables an assessment to be made of the increase of iodine in the thyroid; this increase dropped in correlation with the increase in the amount of iodine given, within the range of dose employed.

Further research will be carried out on more patients in order to establish the possibility offered by this technique in the field of thyroid pathophysiology.