Quantitative 123I-iodide scintigraphy and radiation dosimetry in infants with congenital hypothyroidism.

Quantitative studies of 123I-iodide uptake using a gamma camera were undertaken in 23 infants with congenital hypothyroidism. Background oral radioactivity was reduced by ensuring that the infants drank fruit juice during the study. In 7 cases, there was no evidence of functioning thyroid tissue, in 13 cases, lingual tissue was present, and in 3 cases, there was uptake at the normal thyroid site. Dyshormonogenesis, as shown by a positive perchlorate discharge at 30-60 min after radioiodine administration, was present in 5 of the cases with demonstrable uptake. The estimated 20-min uptake of 123I-iodide was less than 2.6% of the dose in all cases except 1; in this case, the uptake was 10.4%, but this was completely discharged by perchlorate. There was good agreement between the quantitative radioiodine-uptake and -discharge results and the circulating thyroid-hormone levels. The estimated radiation dose to thyroid tissue using the technique was 9.2 mSv for an intravenous administration of 2MBq 123I-iodide.