Tracer: From 3 Different Sources
A radioactive substance that is introduced into the body so that its distribution, processing, and elimination from the body can be monitored.
A compound introduced into the body, the progress of which can subsequently be followed and information obtained about the body’s metabolic activities. Radioactive tracers are compounds labelled with RADIONUCLIDE which give o? radiation. This can be measured with a gamma camera or a scintigram. The information is used in the investigation of suspected tumours in the BRAIN or malfunctioning of the THYROID GLAND.
n. a substance that is introduced into the body and whose progress can subsequently be followed so that information is gained about metabolic processes. Radioactive tracers, which are substances labelled with *radionuclides, give off radiation that can be detected on a *scintigram or with a *gamma camera. They are used for a variety of purposes in *nuclear medicine. See MUGA scan; positron emission tomography; SPECT scanning.
A non-metallic element, the compounds of which are found in all living tissues and which is a constituent (as carbon dioxide) of air exhaled from the LUNGS. Two isotopes of carbon, 11C and 14C, are used in medicine. Carbon-11 is used in positron-emission tomography (see PET SCANNING); carbon-14 is used as a tracer element in studying various aspects of METABOLISM.... carbon
This is a form of a chemical element with the same chemical properties as other forms, but which has a di?erent atomic mass. It contains an identical number of positively charged particles called protons, in the nucleus, giving it the same atomic number, but the numbers of neutrons di?er. A radioactive isotope, or radionuclide, is one that decays into other isotopes, and in doing so emits alpha, beta or gamma radiation.
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
An ISOTOPE of the arti?cial element technetium. It emits gamma rays and is used as a tracer in building up a scintigraphic radioactive image of organs such as the brain.... technetium-99
(radioautography) n. a technique for examining the distribution of a radioactive *tracer in the tissues of an experimental animal. The tracer is injected into the animal, which is killed after a certain period. Thin sections of its organs are placed in close contact with a radiation-sensitive material, such as a photographic emulsion, and observed under a microscope. Blackening of the film indicates a high concentration of radioactive material.... autoradiography
an imaging investigation of a patient’s bone using radioactive *tracers. *Technetium-99m phosphate is injected intravenously and absorbed into the hydroxyapatite crystals of bone. It concentrates in areas of increased blood flow and metabolism, such as areas of infection, trauma, and *neoplasia, and gives off radiation that can be detected by a *gamma camera, thereby producing a map or scan of activity in the target area. A bone scan is particularly useful in the diagnosis of subtle fractures (including stress fractures), avascular necrosis (see osteonecrosis), osteomyelitis, tumour spread (metastasis), and loosening of orthopaedic implants.... bone scan
diethylenetriaminepentaacetic acid, which when labelled with *technetium-99m is used as a tracer to obtain *scintigrams of the kidney over a period of time, by means of a *gamma camera. DTPA is filtered out of the blood by the kidneys and passes into the urine; it is used to show the function of the kidney and reflux from the bladder up the ureter. It is particularly useful in assessing obstruction to urinary drainage from the kidneys.... dtpa
an apparatus that detects gamma rays emitted by radioactive isotopes that have been introduced into the body as *tracers. It contains an activated sodium iodide crystal (see scintillator) and a large array of photomultiplier tubes. Using lead *collimators, the position of the source of the radioactivity can be plotted and displayed on a TV monitor or photographic film (see scintigram).... gamma camera
mercaptoacetyltriglycine: a tracer used in nuclear medicine, during *renography, when labelled with technetium-99m. This agent is cleared by glomerular filtration and tubular secretion by the kidneys. It can be used to measure effective renal plasma flow and to give anatomical information. Compared with a *DTPA scan, it can be used in patients with impaired renal function.... mag3
a radiological technique that enhances visualization of blood vessels (see angiography). A digitized image is taken before the contrast medium (a ‘mask’) is injected, and this is subtracted by computer from the images taken after contrast injection. Only the blood vessels remain on the image. The technique enables blood-vessel anatomy and blood supply to an organ to be demonstrated more clearly. The quality of the image is very dependent on the patient remaining still, since movement causes severe loss of image (movement *artifact). The technique can also be used in nuclear medicine using two different tracers to look for parathyroid gland tumours.... digital subtraction
(lymphography) n. X-ray examination of the lymphatic vessels and lymph nodes after a contrast medium has been injected into them (see angiography). Lymphatic vessels in the upper part of the foot are dissected and cannulated after injecting methylene blue into the web space to identify them. Then a viscous contrast medium (Lipiodol) is injected into them at a very slow rate. Its main uses are in the investigation of the extent and spread of cancer of the lymphatic system, the investigation of lymphoedema, and postoperative collection from lymphatic damage. Newer techniques involve injection of contrast medium directly into the lymph nodes (intranodal lymphangiography). Alternatively, the lymphatic system can be imaged using a gamma camera following the injection of a radioactive tracer. This examination has now largely been replaced by other *cross-sectional imaging techniques.... lymphangiography
Meta-IodoBenzylGuanidine: a radioactive *tracer, labelled with iodine-123 or iodine-131, which binds to adrenergic nerve tissue. With the aid of a gamma camera, it can be used to detect the presence of a range of adrenergic tumours, including *neuroblastoma and *phaeochromocytoma.... mibg
a medical specialty in which *radionuclides (especially *technetium-99m) are used as *tracers to study the structure and function of organs of the body. The radionuclide is attached to a compound suitable for the particular test and then injected, inhaled, or ingested. When concentrated in the organ under investigation, the tracer can be imaged using a *gamma camera, revealing the structure or demonstrating the function of the organ. Alternatively, blood or urine samples may be analysed. See also nuclear cardiology.... nuclear medicine
a technique for demonstrating an abnormal blood supply to an organ by injecting a radioactive *tracer or *contrast medium. One of the most common uses, often in conjunction with ventilation scanning (see ventilation-perfusion scanning), is to detect obstruction of pulmonary arteries due to embolism by thrombus (see pulmonary embolism). Particles labelled with radioactive tracer are injected intravenously and become temporarily lodged in the capillaries in the lungs. Areas not being perfused show up as holes on the gamma-camera images. In *magnetic resonance imaging or *computerized tomography, contrast medium is injected and a series of images is obtained. The rate of change of enhancement is an index of the blood supply to the area of interest. This technique can be used to study blood supply to the brain, heart, or kidneys (in particular), to help diagnose arterial strictures or blockages, or tumours in which blood supply may be increased by abnormal vessels.... perfusion scan
n. a technique using radioactive antibodies as *tracers to estimate the levels of natural substances in a blood sample. The antibodies bind to antigens, and the amount of radioactivity trapped is a measure of the amount of the target antigen present. The technique is widely used in the estimation of hormone levels.... radioimmunoassay
n. an *isotope of an element that emits alpha, beta, or gamma radiation during its decay into another element. Artificial radioisotopes, produced by bombarding elements with beams of neutrons, are widely used in medicine as *tracers and as sources of radiation for the different techniques of *radiotherapy.... radioisotope
n. a substance containing a radioactive atomic nucleus. Radionuclides can be used as *tracers for diagnosis in *nuclear medicine.... radionuclide
(isotope renography) n. the radiological study of the kidneys by a *gamma camera following the intravenous injection of a radioactive *tracer, which is concentrated and excreted by the kidneys. The radioactive isotope (usually *technetium-99m) emits gamma rays, which are recorded by the camera positioned over the kidneys. A graph of the radioactivity in each kidney over time provides information on its function and rate of drainage. See DMSA; DTPA; MAG3.... renography
n. a diagram showing the distribution of radioactive *tracer in a part of the body, produced by recording the flashes of light given off by a *scintillator as it is struck by radiation of different intensities. This technique is called scintigraphy. By scanning the body, section by section, a ‘map’ of the radioactivity in various regions is built up, aiding the diagnosis of cancer or other disorders. Such a record is known as a scintiscan. These images are now usually obtained using a *gamma camera.... scintigram
(in *nuclear medicine) a scan that can help to localize the site of a parathyroid adenoma before surgical removal, to treat primary *hyperparathyroidism. The tracer is technetium-99m-labelled sestamibi (a small protein), which is selectively absorbed by overactive parathyroid glands.... sestamibi parathyroid scan
(single photon emission computing tomography) (in nuclear medicine) a *cross-sectional imaging technique for observing an organ or part of the body using a *gamma camera; images are produced after injecting a radioactive *tracer. The camera is rotated around the patient being scanned. Using a computer reconstruction *algorithm similar to that of a *computerized tomography scanner, multiple ‘slices’ are made through the area of interest. SPECT scanning is used particularly in cardiac nuclear medicine imaging (see MUGA scan). It differs from PET scanning in that radioactive decay gives off only a single gamma ray.... spect scanning
n. an isotope of the artificial radioactive element technetium. It emits gamma radiation only, with no beta particles, at a convenient energy for detection by a *gamma camera and has a short half-life. For these reasons it is widely used in nuclear medicine as a *tracer for the examination of many organs (see scintigram). Symbol: Tc-99m.... technetium-99m
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