Magnetic resonance imaging Health Dictionary

... nuclear magnetic resonance

The air carrying the voice produced in the LARYNX passes through the throat, mouth and nose. The shape and size of these structures will in?uence the timbre of the voice, or vocal resonance. This will vary from person to person and even within an individual; for example, with a cold.... vocal resonance

See MRI.... magnetic resonance imaging(mri)

The lengthening and intensi?cation of sound produced by striking the body over an air-containing structure such as the lung. Decrease of resonance is called dullness and increase of resonance is called hyper-resonance. The process of striking the chest or other part of the body to discover its degree of resonance is called PERCUSSION, and according to the note obtained, an opinion can be formed as to the state of consolidation of air-containing organs, the presence of abnormal cavities, and the dimensions and relations of solid and air-containing organs lying together. (See also AUSCULTATION.)... resonance

Techniques for providing pictures that show the structure or function of bones. X-ray images are the most commonly used technique for diagnosing fractures and injuries. More detailed information is provided by tomography, CT scanning, or MRI, which can show tumours

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

Techniques that provide pictures of the brain; they are used to detect injury or disease and include X-rays, angiography, CT scanning, MRI, PET (positron emission tomography) scanning, and SPECT (single photon emission ). X-ray films can show changes in the skull caused by a fracture or, rarely, by a brain tumour or aneurysm. Angiography shows up the blood vessels in the brain, and is used to investigate subarachnoid haemorrhage, aneurysms, abnormalities of the blood vessels, and other circulatory disorders.

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

Techniques that provide images of heart structure. Imaging is used to detect disease or abnormalities. A chest X-ray, the simplest and most widely used method of heart imaging, shows heart size and shape, and the presence of abnormal calcification. Pulmonary oedema and engorgement of the vessels connecting the heart and lungs are also usually detectable.

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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

See barium X-ray examinations.... intestinal imaging

Techniques that produce images of the liver, gallbladder, bile ducts, and blood vessels supplying the liver, to aid the detection of disease.

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

Techniques that provide images of the lungs to aid in the diagnosis of disease.

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

See barium X-ray examinations.... stomach imaging

see Doppler ultrasound.... colour flow ultrasound imaging

any technique that produces an image in the form of a section through the body with the structures cut across. The main techniques are *ultrasonography, *computerized tomography, *magnetic resonance imaging, and some *nuclear medicine techniques (see positron emission tomography; SPECT scanning). If a series of thin-section images is stacked they can be ‘cut’ through to show other planes or allow reconstruction of three-dimensional images.... cross-sectional imaging

Techniques for visualizing the kidneys, usually performed for diagnosis. Ultrasound scanning can be used to identify kidney enlargement, a cyst or tumour, and the site of any blockage. Conventional X-rays show the outline of the kidneys and most kidney stones. Intravenous urography shows the internal anatomy of the kidney and ureters. Angiography is used to image blood circulation through the kidneys. CT scanning and MRI provide detailed cross-sectional images and can show abscesses or tumours. Two types of radionuclide scanning are used for the kidney: DMSA and DTPA scanning. DMSA is a substance given by intravenous injection that binds to cells in the kidney tubule, giving a single, static picture of the kidneys. DTPA, also given intravenously, is filtered in the kidneys and passes out in the urine. Pictures taken at intervals record its passage through the urinary tract and show kidney function. ... kidney imaging

a variant of *diffusion weighted imaging in which both the direction and the amount of diffusion of water molecules in a tissue are coded in the image. This MRI technique can be valuable in linear structures, such as nerves and muscle fibres. In the brain the major tracts and their communications can be studied with this technique (see tractography).... diffusion tensor imaging

a method of creating images by *magnetic resonance imaging that relies on the amount of available space that individual water molecules have to move in, which depends on the local microstructure. Pathological tissues generally are less organized, with more space for diffusion and a higher signal.... diffusion weighted imaging

(DSI) the production of static images using an *image intensifier, usually during a fluoroscopic examination. The images can be stored digitally (see digitization) and either transferred to photographic film or viewed on a TV monitor.... digital spot imaging

see Doppler ultrasound.... duplex imaging

(fMRI) a type of *magnetic resonance imaging that measures the increased hemodynamic response seen with neural activity in the brain or spinal cord. fMRI has allowed major advances in brain mapping (i.e. matching sections of the brain with particular behaviours, thoughts, or emotions).... functional magnetic resonance imaging

see co-registration.... fusion imaging

n. (in radiology) the production of images of organs or tissues by a range of techniques. These images are used by physicians in diagnosis and in monitoring the effects of treatment. They can also be used to guide *interventional radiology techniques. See also computerized tomography; magnetic resonance imaging; ultrasonography.... imaging

see 3-D magnetic imager.... magnetic imager

(MRS) a diagnostic technique that utilizes the phenomenon of *nuclear magnetic resonance to obtain a biochemical profile of tissues by exciting elements other than hydrogen in water and other body components. It is particularly useful for biochemical analysis of tissues in the living body. This technique is used clinically in the brain and prostate.... magnetic resonance spectroscopy

an emerging area of imaging that exploits recent developments of molecular and cell biology to create new markers. Most molecular imaging uses versions of these markers labelled with radioactive isotopes, which – after administration – are localized in the body and can be detected using such techniques as *positron emission tomography, *SPECT scanning, *magnetic resonance imaging, and optical imaging.... molecular imaging

(rTMS) see transcranial magnetic stimulation.... repetitive transcranial magnetic stimulation

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

an instrument that harnesses magnetic technology to give a virtual image of an endoscope during colonoscopy. It aids steering and minimalizes looping of the endoscope. An external antenna tracks the magnetic field generated by coils built inside the endoscope, enabling real-time 3D imaging of this instrument. Trade name: ScopeGuide.... 3-d magnetic imager

(TMS) stimulation of the brain by strong magnetic fields that induce electric currents in the underlying brain tissue. Repetitive transcranial magnetic stimulation (rTMS), consisting of a series of TMS pulses, is used to treat depression. Its clinical utility is controversial, with inconsistent research results regarding its efficacy. Although there have been some small studies regarding its use with other conditions, such as OCD, rTMS is not currently used routinely in the treatment for any illness other than depression.... transcranial magnetic stimulation

the rapid acquisition and manipulation of ultrasound information from a scanning probe by electronic circuits to enable images to be produced on TV screens almost instantaneously. The operator can place the scanning probe accurately on the region of interest in order to observe its structure and appreciate moving structures within it (see Doppler ultrasound). Using similar techniques, the instantaneous display of other imaging modalities, such as *computerized tomography scanning and *magnetic resonance imaging, can now be achieved. Real-time imaging is useful in guiding *interventional radiology procedures, for example, allowing a needle to be guided accurately as it is passed into the body. It is also useful for observing dynamic physiological activity.... real-time imaging