Ct scanner Health Dictionary

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

The abbreviation for magnetic resonance imaging. is a diagnostic technique that produces cross-sectional or 3-dimensional images of organs and other body structures.

The patient lies inside a scanner surrounded by a large, powerful magnet. A receiving magnet is then placed around the part of the body to be investigated. If large areas, such as the abdomen, are to be imaged, the receiving magnet is fitted inside the scanner; for a smaller area, such as a joint, a magnet may be placed around the part to be scanned. The scanner generates a strong magnetic field, which causes the atoms in the body to line up parallel to each other. Short pulses of radio waves from a radiofrequency source briefly knock the atoms out of alignment. As the atoms realign they emit tiny signals, which are detected by the receiving magnet. Information about these signals is passed to a computer, which builds up an image based on the signals’ strength and location. images can be enhanced by use of a contrast medium to highlight particular body structures, such as tumours and blood vessels.

Images from are similar to those produced by CT scanning but give greater contrast between normal and abnormal tissues. is useful in studying the brain and spinal cord, the internal structure of the eye and ear, the internal organs, and blood flow.There are no known risks or side effects. The technique does not use ionizing radiation and can be performed repeatedly, but the scanner may interfere with the functioning of pacemakers, hearing aids, and other electrical devices.

MRSA The abbreviation for methicillinresistant STAPHYLOCOCCUS AUREUS, a bacterium resistant to methicillin and many other antibiotic drugs. is responsible for the emergence of infections in hospitals that are difficult to treat and can sometimes be fatal.... mri

The abbreviation for positron emission tomography, a diagnostic technique based on the detection of positrons (a type of subatomic particle) that are emitted by radioactively labelled substances introduced into the body. scanning produces 3-dimensional images of the metabolic and chemical activity of tissues.

Substances used in biochemical processes in the body are labelled with radioisotopes and then injected into the bloodstream. The substances are taken up in greater concentrations by tissues that are more metabolically active. The substances emit positrons, which release photons that are detected by the scanner. scans are used to detect brain tumours, locate epileptic activity within the brain, and examine brain function.... pet scanning

A technique by which temperature patterns on the surface of the skin are recorded in the form of an image. Thermography provides clues to the presence of diseases and abnormalities that alter the temperature of the skin, such as problems of the circulation, inflammation, and tumours. There are 2 types of thermography. In one, a camera or scanner picks up infrared radiation naturally emitted from the skin. In the other, sheets of temperature-sensitive liquid crystals are applied to the skin; they change colour in response to changes in temperature.... thermography

n. a sequential set of instructions used in calculations or problem solving. A reconstruction algorithm is a complex mathematical formula used by a computer to construct images from the data acquired by CT, MRI, or other scanners. A diagnostic algorithm or a therapeutic algorithm consists of a stepwise series of instructions with branching pathways to be followed to assist a physician in coming to a diagnosis or deciding on a management strategy, respectively.... algorithm

(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

(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

n. the *SI unit of magnetic flux density, equal to a density of 1 weber per square metre. This unit is important in *magnetic resonance imaging (MRI). Most MRI scanners operate between 0.1 and 2.5 T, but some modern research scanners may go up to 7 T. Symbol: T.... tesla

n. imaging of blood vessels (see also coronary angiography; lymphangiography). In the older form of angiography X-ray imaging was carried out after injection of *radiopaque contrast medium and *digital subtraction applied to enhance visualization. The use of X-rays has now been largely replaced by methods using MRI or CT scanners. Magnetic resonance angiography (MRA) can be performed with (contrast-enhanced) or without (noncontrast) injection of a magnetic resonance contrast agent (see contrast medium). Contrast-enhanced MRA will show the vessels better. These images can be reconstructed in two or three dimensions. Computerized tomographic angiography (CTA) uses a radiographic contrast agent, usually injected into a vein, to increase the visibility of the blood vessels. Fluorescein angiography is a common method of investigation in ophthalmology. *Fluorescein sodium is injected into a vein in the arm, from which it circulates throughout the body. Light of an appropriate wavelength is shone into the eye, causing the dye in the retinal blood vessels to fluoresce. This allows the circulation through the retinal blood vessels to be observed and photographed. Indocyanine green (ICG) angiography uses indocyanine green dye, which fluoresces in infrared light. It is valuable in assessing circulation in the deeper layers of the *fundus.... angiography

(CT) a form of X-ray examination in which the X-ray source and detector (CT scanner) rotate around the object to be scanned and the information obtained can be used to produce cross-sectional images (see cross-sectional imaging) by computer (a CT scan). A higher radiation dose is received by the patient than with some conventional X-ray techniques, but the diagnostic information obtained is far greater and should outweigh the increased risk. CT scanning can be used for all parts of the body. The data obtained can be used to construct three-dimensional images of structures of interest. See also multidetector computerized tomography; spiral CT scanning.... computerized tomography

(MDCT) a development of *spiral CT scanning that uses more than one array of detectors opposite the X-ray tube, so that more tissue can be included, with thinner cuts, in a single rotation of the machine. This is particularly important for three-dimensional reconstruction of tissues. It also allows volumetric scanning or *isotropic imaging, which are best achieved when the thickness of the slice is similar to the size resolution of the detectors in the other two planes. Modern CT scanners are now usually equipped with between 16 and 640 detector arrays. The technique is particularly valuable for imaging fast-moving structures, such as the heart.... multidetector computerized tomography

(PET) a technique in nuclear medicine for *cross-sectional imaging that enables a noninvasive assessment and localization of metabolic activity to be made. Originally used to study activity in the brain, PET is now also used for investigating the chest and abdomen. Emission of a *positron by a radioisotope results in annihilation of the positron on collision with an electron, and the creation of two gamma rays of known energy travelling in exactly opposite directions. The PET scanner has detectors on each side of the patient to detect the simultaneous arrival of the gamma rays. Images are created using reconstruction *algorithms similar to CT scanning. *Fluorodeoxyglucose, labelled with fluorine-18, is used to examine glucose metabolism, and ammonia, labelled with nitrogen-13, gives information on perfusion. Carbon-11 and oxygen-15 can also be used as radioisotopes for PET scanning. Some diseases result in decreased uptake of the radio-labelled material due to decreased function; others show increased glucose metabolism and concentrate the isotope avidly. In this way functional activity of the tissues can be compared with anatomical images obtained by CT or MRI scanning (see PET/CT scanning). Localized areas of increased glucose uptake revealed by PET scans can sometimes signify functional activity of malignant cells, which use more glucose than normal cells, although other processes, such as infection, can produce similar scans. PET scans can help to localize metastatic disease (see metastasis) that is not identified by other scanning techniques. See also tomography. Compare computerized tomography.... positron emission tomography