Radioactive iodine measurement

Potassium iodine tablets can be used to reduce radioactive iodine exposure to the thyroid gland. According to the National Council of Radiation Protection and Measurement (NCRP), taking 130 milligrams of potassium iodine at or before exposure to radioactive iodine effectively blocks nearly 100% of radioactive iodine from reaching the thyroid.1 Waiting 4 hours after exposure to take potassium iodine... 

The release of radioactive iodines from BWR circuits, first into the steam phase and then into the turbine hall, has also been considered thermodynamically (75). A re-analysis of some experimental data of Styrikovich et al (97), suggested that iodates were not, as had been tentatively proposed, likely to be present. Styrikovich s prediction of HIO as a principal species under BWR conditions was confirmed, but it was concluded that his experiments had not measured its steam/water partition coefficient. In view of the meagre experimental evidence, however, more work on this system is desirable. 

Metabolically, radionuclides are handled in the same way as stable elements of the same atomic numher. Thus radioactive iodine simulates stable iodine, being concentrated in the thyroid gland so predictably that its rate of uptake provides an accurate measure of thyroid function. The metabolism of other radionuclides also is sufficiently characteristic so that their patterns of uptake, distribution, translocation, and excretion are similarly predictable. 

Diamino-l,2,4-thiadiazole is devoid of antithyroid activity, as measured by the effect of a single dose on the uptake of radioactive iodine by rat thyroid gland over a 4 hour period.210... 

In other studies of mixing time Mohle and Waeser (Mil) introduced a heat pulse into a vessel and observed the time for two thermocouples in the liquid to indicate the same temperature, but reported only very limited data. Beerbower et al. (B3) added a small amount of radioactive iodine-32, and used Geiger counters to measure the time required to reach a uniform dispersion, for several grease- and asphalt-blending kettles of special design. 

Almost all elements found in nature can now be made radioactive. Radioactive potassium and phosphorus are used as tracers to measure how effectively plants take up fertilizer from soil. Radioactive iodine is applied in nuclear medicine to diagnose and treat thyroid problems. Radiation treatment for cancer therapy uses radioactive cobalt, which is made by irradiating ordinary cobalt with neutrons. 

Serial measurement of Tg is most useful in detecting recurrence of DTC following surgical resection or radioactive iodine ablation. Tg determination is used as an adjunct to ultrasound and scanning. Assessment of serum Tg also aids in the management of infants with congenital hypothyroidism, All patients with hyperthyroidism should have elevated Tg low concentrations of Tg may be an indication that thyrotoxicosis factitia is present. 

The driving force for the development of chemiluminescence-based assays (as well as any other optical or electrical detection methodology) is the replacement of radiolabels both for safety reasons and because of their intrinsic instability. Because the earliest high sensitivity immunoassays utilized antibodies with covalently attached as the label, this has served as a yardstick against which all subsequent assay technologies are measured. For this reason, it is important to understand the detection limits for I. Radioactive iodine is a y-emitter that eventually decays to a stable isotope of lead. The decay process exhibits first-order kinetics so that we can write... 

The antithyroid compounds currently used in the United States are propylthiouracil (6- -propylthiouracil) and methimazole (/-methyl-2-mercaptoimidazole Tapazole). In Great Britain and Europe, carbimazole (Neo-mercazole), a carbethoxy derivative of methimazole, is available, and its antithyroid action is due to its conversion to methimazole after absorption. Measurements of the course of organification of radioactive iodine by the thyroid show that absorption of effective amounts of propylthiouracil follows within 20 to 30 minutes of an oral dose, and that the duration of action of the compounds used clinically is brief. The effect of a dose of 100 mg of propylthiouracil begins to wane in 2 to 3 hours, and even a 500-mg dose is completely inhibitory for only 6 to 8 hours. As little as 0.5 mg of methimazole similarly decreases the organification of radioactive iodine in the thyroid gland, but a single dose of 10 to 25 mg is needed to extend the inhibition to 24 hours. 

A considerable advance in the management of thyroid cancer has resulted from the introduction of recombinant human TSH (thyrogen). A dose of 0.9 mg is administered intramuscularly, followed by an identical dose 24 hours later. The serum thyroglobuLin is then measured 48-72 hours after the second TSH injection this has become the preferred diagnostic test for following patients with differentiated thyroid cancer who have had thyroidectomy and ablation of any remnant tissue with radioactive iodine. This regimen can also be used to stimulate iodine uptake by malignant cells in a total body scan (see below). 

As part of the biogeochemical cycle, the injection of iodine-containing gases into the atmosphere, and their subsequent chemical transformation therein, play a crucial role in environmental and health aspects associated with iodine - most importandy, in determining the quantity of the element available to the mammalian diet. This chapter focuses on these processes and the variety of gas- and aerosol-phase species that constitute the terrestrial iodine cycle, through discussion of the origin and measurement of atmospheric iodine in its various forms ( Sources and Measurements of Atmospheric Iodine ), the principal photo-chemical pathways in the gas phase ( Photolysis and Gas-Phase Iodine Chemistry ), and the role of aerosol uptake and chemistry and new particle production ( Aerosol Chemistry and Particle Formation ). Potential health and environmental issues related to atmospheric iodine are also reviewed ( Health and Environment Impacts ), along with discussion of the consequences of the release of radioactive iodine (1-131) into the air from nuclear reactor accidents and weapons tests that have occurred over the past half-century or so ( Radioactive Iodine Atmospheric Sources and Consequences ). 

Fifteen percent of children with Graves disease will present between 6 and 10 years of age (Wilkins, 1965). Gonsidering drug therapy as a first-line measure for this age group is reasonable. Yet, as 10 years of age is approached, either radioactive iodine or drug therapy can... 

In Europe, in 1998 the EC stated that as a general rule, treatment of thyroid cancer patients using radioactive iodine will only be performed in conjunction with hospitalization of the patient. An activity in the patient should be measured prior to discharge. 

In 1940, Hamilton and associates in Los Angeles and Hertz and his associates in Boston were the first to measure the uptake of radioactive iodine-128 by the thyroid. This made it possible to diagnose patients with increased or decreased thyroidal function. The names, hyper- and hypothyroidism, reflected the functional basis of the diagnosis. The use of radioiodine to define thyroid disease led to the search for other applications of the radioactive tracer principle. 

Two diseases that were defined half a century ago can illustrate a molecular theory of mental disease. The rate of accumulation of radioactive iodine by the thyroid could be measured by radiation detectors pointed at the neck. Patients, who had a disease subsequently called hyperthyroidism were found to have an increased accumulation of radioactive iodine, whereas radioiodine uptake was low in patients with hypothyroidism. Patients with hyperthyroidism were nervousness and anxious, and suffered from weight loss, whereas hypothyroid patients were lethargic and had impaired mental functions. These two diseases illustrate the fundamental principle that if one can measure a chemical process in some part of the body, there will be patients in which the chemical process is abnormally slow, and others in which it is abnormally fast (Fig. 19.1). 

Fig. 19.1 Half a century ago, measurement of radioactive Iodine In the thyroid gland with a Geiger-Mueller counter placed at different points indicated...

The most important prognostic factor for all types of thyroid carcinoma is the TNM status including the invasion of blood and lymph vessels and metastatic spread. For the monitoring of thyroid carcinoma two methods are usually used the nuclear body-scan with radioactive iodine and measuring of serum thyroglobulin, but we have to consider that both methods can reliably detect systemic metastatic spread or relapse of thyroid carcinoma only, if thyroid tissue has been completely removed. 

LS counters are suitable for measuring radionuclides that emit only very low-energy beta particles or electrons, notably tritium (Emax = 18.6 keV). When tritium is measured as tritiated water and its activity is reported relative to water weight or volume, no yield measurement is needed. Liquid samples, e.g., water from the environment, process streams, urine, or dissolved solids, can be counted directly or purified by distillation. Results for purified samples are more reliable to the extent that the radioelement can be identified, quenching is stabilized, and luminescent contaminants are removed. Reagents may have to be added to the distillation flask to hold back other potentially volatile radionuclides, such as radioactive iodine, carbon, ruthenium, or technetium. 

Measurement of the thyroid uptake of radioactive iodine has for many years been a useful supplement to thyroid function tests on blood. While thyroid uptake tests are not usually part of the services oflFered by a clinical chemistry department, they should always be considered in relation to the clinical chemistry tests, and therefore a brief discussion on them is relevant in this review. 

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