Isotope scanning Health Dictionary

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

Positron-emission tomography is a NUCLEAR MEDICINE diagnostic technique that works by identifying positrons – positively charged electrons – given o? by substances labelled with radioactive varieties of elements. The result is three-dimensional images that identify metabolic and chemical activities of tissues, especially brain tissues. The images provide information about tissue and organ functions, and can be collated with structural images using COMPUTED TOMOGRAPHY or magnetic resonance imaging (MRI). The equipment is very expensive and available only in selected hospitals in the United Kingdom. The technique is especially valuable in the assessment of neurological disorders.... pet scanning

A speech disorder in which articulated syllables are wrongly spaced and each is given the same vocal emphasis. The condition occurs as a result of disease in the cerebellum (see BRAIN) or its connecting nerves. (See also VOICE AND SPEECH.)... scanning speech

Ways of producing images of body organs that record, process and analyse sound waves, radio waves or X-RAYS passing through or generated by the body’s tissues. ULTRASOUND scanning using high-frequency, inaudible sound waves directed at the area of the body being studied is the most generally used scanning procedure. Sound waves are re?ected more powerfully by some structures than others, and a pattern of those re?ections is detected and shown on a screen. Other screening methods include COMPUTED TOMOGRAPHY, magnetic resonance imaging (MRI), positron emission tomography (PET SCANNING) and RADIONUCLIDE scanning, which measures the di?erential uptake of radioactive materials in the body’s tissues.... scanning techniques

An abbreviation for computerized axial tomographic scanning, commonly known as CT scanning.... cat scanning

See radionuclide scanning.... radioisotope scanning

Techniques, such as radionuclide scanning and ultrasound scanning, that are used to provide information about the location, anatomy, and function of the thyroid gland.... thyroid scanning

(NT scanning) an ultrasound screening test performed during pregnancy at 11 weeks of gestation that measures the maximum thickness of the translucency between the skin and the soft tissue overlying the cervical (neck) region of the spine of the fetus. Increased NT is associated with an increased risk of chromosomal abnormalities and of a wide variety of structural abnormalities (e.g. heart defects). See also ultrasound marker.... nuchal translucency scanning

an imaging system that allows a PET scan (see positron emission tomography) and a CT scan (see computerized tomography) to be performed very close together, with minimal movement of the patient between scans. This means that the images produced can be co-registered (see co-registration), giving very accurate anatomical localization (from the CT scan) of areas of increased activity (identified on the PET scan). This is very important for determining the site of disease in order to plan treatment.... pet/ct scanning

see ophthalmoscope.... scanning laser ophthalmoscope

(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

A diagnostic technique in which the combined use of a computer and X-rays passed through the body at different angles produces cross-sectional images of tissues. (computed tomography) scanning has revolutionized the diagnosis and treatment of tumours, abscesses, and haemorrhages in the brain, as well as head injuries and strokes. scanning is also used to locate and image tumours, investigate diseases, and aid needle biopsy in organs of the trunk.

Newer types of scanners use a spiral technique: the scanner rotates around the body as the patient is moved slowly forwards on a bed, causing the X-ray beams to follow a spiral course. The computer produces 3-D images. Injected or swallowed contrast media (chemicals opaque to X-rays) may be used to make certain tissues more visible.... ct scanning

A diagnostic technique based on detection of radiation emitted by radioactive substances introduced into the body. Substances are taken up to different degrees by different tissues, allowing specific organs to be studied. For example, iodine is taken up mainly by the thyroid gland, so by “tagging” a sample of iodine with a radioactive marker (radionuclide), the uptake of iodine can be monitored to investigate the functioning of the gland. A radionuclide is swallowed or injected into the blood and accumulates in the target organ. It emits radiation in the form of gamma radiation, which is detected by a gamma camera to produce an image. Cross-sectional images (“slices”) can be obtained using a computer-controlled gamma camera that rotates around the patient. This specialized form of radionuclide scanning is known as (single photon emission computed tomography). Moving mation on blood flow, the movement of the heart walls, the flow of urine through the kidneys, and bile flow through the liver.

Radionuclide scanning is a safe procedure, requiring only minute doses of radiation that are excreted within hours. The radionuclides carry virtually no risk of toxicity or hypersensitivity.... radionuclide scanning

A diagnostic technique in which very high frequency sound waves are passed into the body and the reflected echoes analysed to build a picture of the internal organs or of a fetus in the uterus. The procedure is painless and considered safe.Ultrasonic waves are emitted by a transducer, which is placed on the skin over the part of the body to be viewed. The transducer contains a crystal that converts an electric current into sound waves. These pass readily through soft tissues and fluids, making this procedure useful for examining fluid-filled or soft organs.

One of the most common uses of ultrasound is to view the uterus and fetus, at any time during pregnancy, but often at 18–20 weeks. The age, size, and growth rate of the fetus can be determined; multiple pregnancies detected; and certain problems, such as neural tube defects, diagnosed. Scans may be taken early in pregnancy if problems, such as an ectopic pregnancy, are suspected.

Ultrasound scanning can also be used in newborn babies to examine the brain through a gap in the skull (for example, to investigate hydrocephalus). Ultrasound can help to diagnose disorders such as cirrhosis, gallstones, hydronephrosis, and pancreatitis, as well as problems in the thyroid gland, breasts, bladder, testes, ovaries, spleen, and eyes. The technique is also used during needle biopsy to help guide the needle.Doppler ultrasound is a modified form of ultrasound that uses the Doppler effect to investigate moving objects.

This can be used to examine the fetal heartbeat and to obtain information about the rate of blood flow in vessels.... ultrasound scanning

(helical CT scanning) a development of conventional *computerized tomography (CT) scanning in which the X-ray tube rotates continuously around the patient as he or she passes through the scanner. This allows the acquisition of images throughout a specified volume of tissue much more quickly. Since these images are digitally acquired (see digitization), *post-processing can produce images in numerous planes, without further exposure of the patient to ionizing radiation. See also multidetector computerized tomography.... spiral ct scanning

a technique to image the parathyroid glands. Technetium is taken up only by the thyroid gland, but thallium is taken up by both the thyroid and parathyroid glands. *Digital subtraction of the two isotopes leaves an image of the parathyroid glands alone. It is an accurate technique (90%) for the identification of adenomas of the parathyroid glands secreting excess hormone.... thallium-technetium isotope subtraction imaging

(V/Q scanning) a nuclear medicine technique in which two different isotopes are used, one inhaled (usually *xenon-133 or *krypton-81m), to examine lung ventilation, and the other injected into a vein, to examine lung perfusion. In *pulmonary embolism, the area of lung supplied by the blocked artery is not being perfused with blood – which gives a perfusion defect on the film – but has normal ventilation. This technique is highly sensitive for pulmonary embolism.... ventilation-perfusion scanning