The radio-isotope (see ISOTOPE) thallium201 is used as a tracer during special imaging studies of blood ?ow through the heart muscle in the diagnosis of myocardial ischaemia (see HEART, DISEASES OF.)... thallium
Applications of radionuclides to diagnosis The use of radionuclides in diagnosis is based on the fact that it is possible to tag many of the substances normally present in the body with a radioactive label. Certain synthetic radioactive elements, such as technetium, can also be used. Because it is possible to detect minute quantities of radioactive material, only very small doses are needed, making the procedure a safe one. Furthermore the body pool of the material is therefore not appreciably altered, and metabolism is not disturbed. Thus in studies of iodine metabolism the ratio of radioactive atoms administered to stable atoms in the body pool is of the order of 1:1,000 million. By measuring radioactivity in the body, in blood samples, or in the excreta it is possible to gain information about the fate of the labelled substance, and hence of the chemically identical inactive material. Therefore it is theoretically possible to trace the absorption, distribution and excretion of any substance normally present in the body, provided that it can be tagged with a suitable radioactive label.
If the investigation necessitates tracing the path of the material through the body by means of external counting over the body surface, it is obviously essential to use an isotope that emits gamma radiation or positrons. If, however, only measurements on blood sample or excreta are required, it is possible to use pure beta emitters. Whole-body counters measure the total radioactivity in the body, and these are of great value in absorption studies.
Moving images can provide information on body functions such as the movements of the heart, blood ?ow, bile ?ow in the liver, and urine in the kidneys. The development of COMPUTED TOMOGRAPHY or CT scanning has replaced radionuclide scanning for some imaging procedures.
Five main groups of diagnostic uses may be de?ned:
(1) METABOLIC STUDIES The use of radioactive materials in metabolic studies is based on the fundamental property that all isotopes of an element are chemically identical. The radioactive isotope is used as a true isotope tracer – that is, when introduced into the body (in whatever form) it behaves in the same way as the inactive element. For example, isotopes of iodine are used to measure thyroid function (see THYROID GLAND), and isotopes of calcium enable kinetic studies of bone formation and destruction to be performed.... isotope
cavities; it may be red or yellow. Red bone marrow is present in all bones at birth and is the factory for most of the blood cells. During the teens, red bone marrow is gradually replaced in some bones by less active yellow marrow. In adults, red marrow is confined chiefly to the spine, sternum, (breastbone), ribs, pelvis (hip-bones), scapulae (shoulderblades), clavicles (collarbones), and bones of the skull.
Stem cells within the red marrow are stimulated to form blood cells by the hormone erythropoietin.
Yellow marrow is composed mainly of connective tissue and fat.
If the body needs to increase its rate of blood formation, some of the yellow marrow will be replaced by red.
Sometimes marrow fails to produce sufficient numbers of normal blood cells, as occurs in aplastic anaemia (see anaemia, aplastic) or when marrow has been displaced by tumour cells.
In other cases, marrow may overproduce certain blood cells, as occurs in polycythaemia and leukaemia.... bone imaging
Ultrasound scanning, CT scanning, and MRI are commonly used.
Radionuclide scanning may reveal cysts and tumours and show bile excretion.
X–ray techniques include cholangiography, cholecystography, and ERCP (endoscopic retrograde cholangiopancreatography).
In these procedures, a contrast medium, which is opaque to X-rays, is introduced to show abnormalities in the biliary system.
Angiography reveals the blood vessels in the liver.... liver imaging
Most lung disorders can be detected by chest X-ray.
CT scanning and MRI play an important role in detecting the presence and spread of lung tumours.
Ultrasound scanning is sometimes used to reveal pleural effusion.
Radioisotope scanning is used to detect evidence of pulmonary embolism.... lung imaging
scanning gives images of the brain substance; it gives clear pictures of the ventricles (fluid-filled cavities) and can reveal tumours, blood clots, strokes, aneurysms, and abscesses. is especially helpful in showing tumours of the posterior fossa (back of the skull). and scanning are specialized forms of radionuclide scanning that use small amounts of radioactive material to give information about brain function as well as structure. They enable
blood flow and metabolic activity in the brain to be measured.
Ultrasound scanning is used only in premature or very young babies since ultrasound waves cannot penetrate the bones of a mature skull.... brain imaging
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Echocardiography is useful for investigating congenital heart defects and abnormalities of the valves or heart wall. An ultrasound technique using the Doppler effect allows measurement of blood flow through valves. Radionuclide scanning and CT scanning provide information about the efficiency of heart function. Angiography may be used to show the heart chambers and to assess the condition of the coronary arteries and valves. High-quality images of the heart can be obtained by MRI.... heart imaging
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