[Measurement of thyroidal iodine concentration by in vivo x-ray fluorescent analysis, with special reference to clinical usefulness of the method].

With the purpose of evaluating the clinical usefulness of measuring thyroidal iodine concentrations and contents, a simple apparatus was designed and constructed for in vivo x-ray fluorescent analysis. The apparatus consists of an Am-241 exciting source(300 mCi) and pure Ge detector(50 mm2 X 5 mm) for measuring K alpha fluorescent x-rays(28.3 and 28.6 KeV) emitted from exited iodine. A diversing collimator was so designed that most of one lobe of the thyroid is within the field of view. Counting was usually continued for 4--5 minutes on each lobe to obtain the sensitivity of 0.2 mg/g allowing 30% coefficient of variation. Iodine concentrations measured in 34 resected normal thyroids at autopsy ranged from 0.19--1.34 mg/g with a mean of 0.53 mg/g(male 0.48 +/- 0.19 mg/g, female 0.60 +/- 0.32 mg/g m. +/- 1.s.d.). The results correlated well with the measurement of the same thyroids by activation analysis(r = 0.93). In vivo measurement was performed on healthy volunteers including 16 males and 14 females. Iodine concentrations measured on each lobe of the thyroid revealed 0.40 +/- 0.24 mg/g for males and 0.67 +/- 0.29 mg/g for females. Eighty-four measurements were performed on 80 patients with various thyroidal diseases. Iodine concentrations were low in chronic thyroiditis(0.06 +/- 0.13 mg/g) and sub-acute thyroiditis(0.28 +/- 0.12 mg/g). Most patients with Graves' disease showed normal or low iodine concentrations (0.47 +/- 0.29 mg/g) regardless of status of treatments (pre-, under- or posttreatment) or thyroidal function. Twenty-one measurements were performed on 21 patients with nodular goiter. Nodule/Gland ratio of I-127 concentration was 0.78 +/- 0.47 in 17 patients with cold nodule, and it ranged from 1.2--1.9 in 4 patients with hot nodule.