Thyroid scan

In multinodular goiters, a thyroid scan shows patchy areas of autonomously functioning thyroid tissue. 

Thyroid scans with 1l]I are useful in determining the activity of thyroid nodules in the intact thyroid gland. A nonradioactive, cold nodule indicates a higher risk of thyroid carcinoma, but the scan alone is not recommended as a technique of selecting patients for surgery. After removal of a thyroid carcinoma, a scan of the neck may demonstrate areas of increased activity in the cervical lymph nodes and other organs, indicating metastatic disease. 

Thyroid scanning II Reversible anion uptake Tc04 551... 

A retrospective record review of 300 patients with Graves disease and 100 with silent thyroiditis who had undergone thyroid scans showed that the likelihood of lithium exposure was 4.7 times higher in the latter, suggesting a link between lithium and thyrotoxicosis caused by silent thyroiditis (649). 

Andros G, Harper PV, Lathrop KA, McCardle RJ (1965) Pertechnetate-99m localization in man with application to thyroid scanning and the study of thyroid physiology. J Clin Endocrinol... 

Sodium pertechnetate Tc-99m was introduced for scanning the thyroid (Harper 1964) and for brain scanning (McAfee et al. 1964 Quinn 1965), primarily because of its physical properties other applications followed (Harper et al. 1966). The striking similarity of the heptavalent anion with iodide, however, has made pertechnetate an excellent radionuclide for thyroid scanning and for the study of thyroid physiology (Andros et al. 1965 Kusic et al. 1990). 

Montelibano EB, Ford DR, Sayle BA (1979) Altered Tc-99m pertechnetate distribution in a thyroid scan after Tc-99m pyrophosphate administration. Clin Nucl Med 4 277-278 Oldendorf WH, Sisson WB, lisaka Y (1970) Compartmental redistribution of " Tc-pertechnetate in the presence of perchlorate ion and its relation to plasma protein binding. J Nucl Med... 

Although iodine has several radioactive isotopes, greatest use has been made of I. It has a half-life of 8 days therefore, more than 99% of its radiation is expended within 56 days. Its radioactive emissions include both y rays P and particles. The short-lived radionuclide of iodine, I, is primarily a y-emitter with a half-life of only 13 hours. This permits a relatively brief exposure to radiation during thyroid scans. 

Figure 23.9 The use of a radioisotope to image the thyroid giand. Thyroid scanning is used to assess nutritionai deficiencies, inflammation, tumor growth, and other thyroid-related ailments. In 1 scanning, the thyroid gland absorbs " 1 ions whose (3 emissions expose a photographic film. The asymmetric shape revealed in the image indicates disease.

Tc is used for diagnostic purposes for liver, spleen, and thyroid scanning ( 9.5). The Mo parent, obtained by chemical separation from fission product mixture, is absorbed on a column of alumina and the daughter "Tc removed by passage of saline solution at intervals governed by the equilibrium. The parent, when it is fixed in a semipermanent sample as on an adsorbent column, is often known as a cow and the... 

We are constantly exposed to background radiation from cosmic radiation (interaction of energy from the sun with the earth s atmosphere), terrestrial radiation from breakdown of uranium in the soil, and natural internal radiation in our bodies from carbon-14 that is present at birth. Man-made radiation sources include diagnostic X-rays, nuclear medicine (bone scans, thyroid scans, etc.), radiation therapy for cancer, nuclear power facilities, and nuclear weapons. 

The main diagnostic practices with radiopharmaceuticals are the procedures for bone, cardiovascular, lung perfusion, lung ventilation, thyroid scan, thyroid uptake, renal, liver/ spleen, and brain examinations. The effective doses per procedure are considerably higher and are 4.5 mSv, 8 mSv, 1.5 mSv, 1 mSv, 3.4 mSv, 15 mSv, 1.9 mSv, 1.7 mSv, and 6 mSv, respectively, and the number of procedures per 1,000 population are 4.5, 2.7, 1.8, 0.34, 4.1, 0.92, 0.89, 2.1, and 1.3, respectively for countries at health-care level I. But patients near to the end of their lives receive many of these exposures, and thus the doses are not distributed evenly among the population. Therefore, these doses should not be used for the assessment of detrimental effects of radiation exposure. 

Figure 10.6 A thyroid scan produced after the administration of a radioactive iodine isotope. Is either a hot spot or a cold spot present ...

Other candidate areas for biological monitoring include the screening of individuals exposed to iodine-125 or -131 (thyroid scans or urine levels), and monitoring urine for tritium levels. Further information on monitoring of radiological agents can be found in Chapter 13. 

Hoffer PB, Jones WB, Crawford RB, Beck R., Gottschalk A. 1968. Fluorescent thyroid scanning a new method of imaging the thyroid. Radiology 90 342-344. 

Hoffer PB, Gottschalk A. 1971. Fluorescent thyroid scanning scanning without radioisotopes. Radiology 99 117-123. 

Fig. 12 (a) Normal 99Tcm thyroid scan, (b) Kix iodine peak from same patient during XEF study. 

Alterations in background by contamination with other frequently used radioisotopes Since fluorescent thyroid scans are often performed to evaluate further the findings initially obtained from a pertechnetate or sodium iodide scan, the effect of these radioisotopes on quantitation and imaging of iodine distribution was evaluated by x-ray fluorescence. Figure 9 shows the 99mTc spectrum with the source shutter of the instrument closed. 

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