The in vivo measurement of the total iodine content of the thyroid gland by x-ray fluorescence.

An accurate, in vivo Am-241 excited x-ray fluorescence techniques was investigated for exploring the correlation between thyroid iodine content (TIC) and various thyroid disorders. The correction for fluorescent x-ray absorption by overlying tissues was made by using the x-ray to gamma ray peak ratio from administered I-123 as an index of thyroid gland depth. In a series of phantom studies, TIC was measured with an uncertainty of +/- 11%, and the depth correction added another +/- 26% error. Radiation doses to the patient were estimated with TLD measurements to be about 15 mrem from I-123, and 13 mrem from Am-241.