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Appendix H Glossary basal metabolism The energy required to keep the body functioning at rest. beta particles Charged particles emitted from the atomic nucleus during radioactive decay. Beta particles are identical to electrons. li3i emits beta particles. cholesterol Chemically a lipid; also an important constituent of body cells; also, among other functions, involved with the formation of hormones. colloid A type of liquid similar to a suspension. Thyroid hormones are stored in thyroid gland in the form of colloid. conversion ratio A factor used to convert amount of radioactivity administered to absorbed dose in tissue. dose conversion See conversion ratio. dosunetry Measurement of absorbed dose. A way to monitor amount of radiation exposure. E-6 Shorthand for lo-6 = I/1,000,000 (one in a million) estrogen A group of hormones essential for normal female sexual development and for the healthy functioning of the female reproductive system. excess risk The risk over and above the natural risk that may be attributable to exposure to some agent. excretion The discharge of waste material from the body. extracellular fluid Fluid that exists outside a cell. 101

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102 The ALL Thyroid Function Study follicular cells Cells of thyroid glands engaged in production of thyroid hormone. gamma radiation Very-short-wavelength, high-energy electromagnetic radiation emitted by radioactive material during radioactive decay. Geiger-Muller tube A device used to measure beta particles and gamma rays. half-life A property of radioactive atoms. The half-life is a measure of the rate of decay and is the tune necessary for a quantity of radioactive atoms to decay to one-half of the original number. ]~31 has a half-life of eight days. hyperthyroidism A condition caused by excessive secretion of the thyroid hormones, which increases the basal metabolic rate and causes an increased demand for nutrients and oxygen to support this metabolic activity. hypothyroidism A condition due to deficiency of thyroid secretion. (This ~131 130 125 123 initiated cell isotope iodide . . mlcrocune milliliter condition results in lowered basal metabolism, i.e., obesity ~ Radioactive isotope of iodine with an atomic weight of . ~ . Radioactive isotope of iodine with an atomic weight of 130. Radioactive isotope of iodine with an atomic weight of 125. Radioactive isotope of iodine with an atomic weight of 123. An activated cell. Fonns of an element with the same number of protons in the nucleus and thus the same chemical properties. li30, Phi, and }~23 are isotopes of iodine. A compound of iodine with another element, e.g., potassium iodide or sodium iodide. Amount of radioactivity; ~ curie is equal to 37 billion disintegrations per second (dps). ~ microcurie = I/1,000,000 of ~ curie = 37,000 lips. Unit of volume. ~ milliliter = I/1,000 of ~ liter.)

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Appendix H mCi observed risk oocyte protein-bound thyroid . . rat station red . . rat lolmmunoassay radionuclides radiopharmaceuticals renal insufficiency retention rate reverse T; roentgen scaler scintillation counter standard capsule standard error 103 ~ mCi = millicurie = I/1,000 of ~ curie. (See . mlcrocurle.) The risk of incidence or mortality of a disease that has been determined through observation or epidemiological studies. The early or prunitive ovum (before it has developed completely). Thyroid hormones bound to serum proteins. Energy in the form of waves or particles. Unit of absorbed dose. (See cGy. ~ red = ~ cGy.) A laboratory technique that employs a radioactive isotope to measure the concentration of specific substances in blood. A nuclide (a species of atom with a given number of neutrons and protons in its nucleus) that is radioactive. Drugs or medicines that contain a radionuclide. The reduction in the ability of the kidneys to filter waste products from the blood and excrete them in the urine, to control the body's water and salt balance, and to regulate the blood pressure. The rate at which a substance is maintained in living tissue before being removed by excretion or other processes. An amino acid, an inactive metabolite of T4. Unit of radiation exposure. An electronic device that can be used with a radiation detector to measure radiation. A radiation detector used to measure li31 in bodily fluids (e.g., blood). A fonnulation of ll31 containing a Mown amount of }~3 (usually 50-65 microcuries of lisle. A measure of statistical variability of a number of measurements about the mean.

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104 The ALL Thyroid Function Study Tc-99m Technium 99, a radioactive substance commonly used in nuclear medicines. threshold A dose below which an effect is not observed. thyroxine A honnone produced by the thyroid gland. tracer dose A quantity of radioactive material too small to cause adverse health effects. triiodothyronine One of two fonns of the principal hormone secreted by the thyroid gland. T3 One of the hormones made in the thyroid. It is also produced in extrathyroidal tissues such as the liver and kidney. T4 One of the hormones made in the thyroid. ,uCi Shorthand for microcurie. uptake The process of a tissue or organ accumulating a particular compound or substance. Thyroid uptake refers to accumulation of iodine in the thyroid gland.