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Wednesday, December 23, 2009

NUCLEAR MEDICINE-IN VITRO, IN VIVO TESTS-LESSON 141



NUCLEAR MEDICINE TESTS:
Procedures: Nuclear medicine physicians use two types of tests in the diagnosis of disease. In vitro (in the test tube) procedures and in vivo (in the body) procedures. In vitro procedures involve analysis of blood and urine specimens using radioactive chemicals. For example, a radioimmunoassay (RIA) is an in vitro procedure that combines the use of radioactive chemicals and antibodies to detect hormones and drugs in a patient's blood. The test allows the detection of minute amounts of drug. RIA is used to monitor the amount of digitalis, a drug used to treat heart disease in a patient's bloodstream and can detect hypothyroidism in newborn infants.
In vivo tests trace the amounts of radioactive substances within the body. They are given directly to a patient to evaluate the function of an organ or to image it. For example, in tracer studies a specific radionuclide is incorporated into a chemical substance and administered to a patient. The combination of the radionuclide and a drug or chemical is called a radiopharmaceutical or labeled compound. Each radiopharmaceutical is designed to concentrate in a certain organ. The organ can then be imaged with the radiation given off by the radionuclide.
A sensitive external detection instrument called scintillation scanner is used to determine the distribution and localization of the radiopharmaceutical in various organs, tissues, and fluids. The amount of radiopharmaceutical at a given location is proportional to the rate at which the gamma rays are emitted. Nuclear medicine studies depict the physiological behavior (how the organ works) rather than the specific anatomy of an organ.
The procedure of making an image to follow the distribution of radioactive substance in the body is called scanning. The image produced is called scan. Uptake refers to the rate of absorption of the radiopharmaceutical into an organ or tissue.
Radiopharmaceuticals may be administered by many different routes to obtain a scan of a specific organ in the body. For example, in the case of a lung scan, the radiopharmaceutical can be given intravenously (perfusion studies, which rely on passage of the radioactive compound through the capillaries of the lungs) or by inhalation of xenon-133 gas (ventilation studies), which fills the air sacs (alveoli). The combination of these tests permits sensitive and specific diagnosis of clots in the lung (pulmonary emboli).
In the next lesson we will learn about diagnostic procedures that utilize radionuclides. Okay.

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