Radiopharmacokinetics and radiation absorbed dose calculations from 131I-meta-iodobenzylguanidine (131I-MIBG).

In connection with clinical 131I-MIBG studies of patients with suspected pheochromocytoma and adrenomedullary hyperplasia quantitative biokinetic data have been collected in order to improve the present estimations of absorbed dose to various organs and tissues. Whole-body profiles as a function of time were measured with a whole-body counter. The retention in the total body and in the thyroid gland could be derived from the measured whole-body profiles by summing up the corresponding values. The retention of 131I-MIBG could not be exactly measured for further organs from the whole-body profiles in man. For this reason animal studies were performed with mice. The biokinetic animal data were transferred to man in form of the cumulative activity for the various organs. The mean absorbed dose for selected organs per injected activity unit was calculated using the concept of absorbed fractions (MIRD method) taking into account the radioactivity within the remaining body. Except for both the adrenal medulla and the thyroid gland the absorbed doses for all the other selected organs are in a range from 0.108 mGy MBq-1 for the testes to 0.176 mGy MBq-1 for the lungs. The absorbed dose to the thyroid gland amounts to the considerable value of 5.69 mGy MBq-1 although the thyroid gland was blocked. The greatest absorbed dose was estimated for the normal adrenal medulla with 18.67 mGy MBq-1.

Comparison of autoantibodies level in thyroid autoimmune diseases estimated by different methods.

Autoantibodies to different thyroid cell components in serum of patients with thyroid disease have been estimated by several methods. The TSH receptor antibodies (TRAb) have been detected in 77% of untreated Graves-Basedow, in 70% of thionamide drugs treated Graves-Basedow patients up to four months of the treatment and in 48% of patients with Hashimoto's thyroiditis. Microsomal antibodies (MAb) and thyroid plasma membrane antibodies (ATMA) have been detected in 84% and 68% respectively, in thionamide drugs treated Graves-Basedow and in 91% and 72% in Hashimoto's thyroiditis. The thyroglobulin antibodies have been detected in 42% of untreated Graves-Basedow, in 47% of thionamide drugs treated Graves-Basedow and in 77% of Hashimoto's thyroiditis. In 19% to 21% of patients with toxic nodular goiter underlying autoimmunological process have been established by the detection of high levels of serum autoantibodies (ATMA and MAb). In the non-toxic nodular goiter, non-thyroid autoimmune diseases and healthy blood donors only thyroglobulin antibodies were detected in a significant number of patients. Other types of antibodies (ATMA or MAb) were detected only in sporadic cases of non-thyroid autoimmune diseases.

[Detection of antibodies against thyroid gland membranes]. / Nachweis von Antikörpern gegen Schilddrüsenmembranen.

We present an enzyme immunoassay for the determination of thyroid membrane bound antibodies. This assay can help to differentiate autoimmune and non-autoimmune thyroid diseases. We used 101 sera and compared our results with these of commercial assay kits. In this form we estimate with our test more than one thyroid antibody, but we found a good correlation especially to the microsomal antibody. We can give the results as an index at a constant serum dilution or in titers.

Radiopharmacokinetics and radiation dose from 99mTc-HM-PAO (preliminary report).

Whole body retention measurements were performed in volunteers after i.v. injection of 99mTc-HM-PAO (Ceretec). The organ accumulation was measured in mice and data were transferred to standard man according to ICRP. Absorbed dose calculations were made with these data by using the concept of absorbed fractions (MIRD method). In man, the whole body retention and the retention in the brain could be calculated by direct measurement, absorbed doses to the other organs could only be derived from animal data. The absorbed dose to the brain derived from human data (10.3 microGy/MBq) is greater by a factor of 2 than that derived from animal data. The highest absorbed dose was received by the thyroid (24.4 microGy/MBq), the absorbed dose to the ovaries, testes and whole body ranged from 2.8 to 4.2 microGy/MBq.