B-scan: From 1 Different Sources
examination of the tissues of the eye in cross section by means of a high-frequency ultrasound machine. It is useful in the diagnosis of eye disease, especially in the posterior segment of the eye when direct viewing is obscured (e.g. by dense cataracts). See also A-scan.
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 image produced by one of several scanning techniques.... scan
See COMPUTED TOMOGRAPHY.... ct scan
The machine which combines the use of a computer and X-rays to produce cross-sectional images of the body (see COMPUTED TOMOGRAPHY).... ct scanner
An abbreviation for computerized axial tomographic scanning, commonly known as CT scanning.... cat scanning
Dual-energy X-ray absorptiometry, a technique that measures bone density by passing beams of lowdose radiation through bone. scans are used to assess the severity of osteoporosis. (See also densitometry.)... dexa scan
A type of kidney imaging technique (see radionuclide scanning).... dmsa scan
See radionuclide scanning.... isotope scanning
Ultrasound scanning performed in early pregnancy in order to identify fetuses at high risk of chromosomal abnormalities such as Down’s syndrome. The scan investigates the nuchal fold, an area of skin at the back of the neck. Excessive thickness of the skin is an indicator of possible chromosomal abnormalities.... nuchal thickness scan
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
n. examination of ocular tissue, including measurement of the length of the eye (axial length), by means of a high-frequency ultrasound machine. See also B-scan.... a-scan
(multiple-gated acquisition scan) a technique used in *nuclear medicine for studying the left-ventricular function and wall motion of the heart. The patient’s red cells are labelled with radioactive technetium-99m. A gamma camera, connected to an ECG, collects information over a prolonged period for each phase of heart movement (ECG gating) to form an image of the blood pool within the heart at specific points in the cardiac cycle. Tomographic reconstructions can be made to give cross-sectional images of the heart in different phases of the cardiac cycle, using reconstruction *algorithms comparable to CT scanning (see SPECT scanning).... muga scan
(thallium scan) a method to detect and quantify myocardial *ischaemia. An intravenously injected *radionuclide that is taken up by normal heart muscle can be imaged using a *gamma camera. Areas of scar due to *myocardial infarction emit little or no radioactivity and are seen as ‘cold spots’. Exercise is mimicked by infusing drugs to increase the heart rate in order to provoke cold spots in the diagnosis of ischaemic heart disease.... myocardial perfusion scan
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
(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
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
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
(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
(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
see myocardial perfusion scan.... thallium scan
(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
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