tomography /to·mog·ra·phy/ (to-mog´rah-fe) the recording of internal body images at a predetermined plane by means of the tomograph.
tomography
tomography (tōmog´r
fē),
tomography
computed tomography (CT), computerized axial tomography (CAT) an imaging method in which a cross-sectional image of the structures in a body plane is reconstructed by a computer program from the x-ray absorption of beams projected through the body in the image plane.
positron emission tomography (PET) a nuclear medicine imaging method similar to computed tomography, except that the image shows the tissue concentration of a positron-emitting radioisotope.
single-photon emission computed tomography (SPECT) a type in which gamma photon–emitting radionuclides are administered and then detected by one or more gamma cameras rotated around the patient, using the series of two-dimensional images to recreate a three-dimensional view.
ultrasonic tomography the ultrasonographic visualization of a cross-section of a predetermined plane of the body.
to·mog·ra·phy (t -m g r -f )n. Any of several techniques for making detailed x-rays of a plane section of a solid object, such as the body, while blurring out the images of other planes. Also called laminagraphy, planigraphy, planography, stratigraphy. to  mo·graphic (tm-gr f k) adj. |
tomography
[təmog′rəfē]
Etymology: Gk, tome + graphein, to record
1 sectional imaging.
2 a radiographic technique in which the tube and film are moved synchronously during exposure, producing a blurred radiograph in which objects within the focal plane are seen more clearly than objects outside the focal plane.
3 a radiographic technique that produces a film representing a detailed cross section of tissue at a predetermined depth. It is a valuable diagnostic tool for the discovery and identification of space-occupying lesions such as might be found in the brain, liver, pancreas, and gallbladder. See also computed tomography, positron emission tomography.
tomography (tōmog´r
fē),n a radiographic technique that produces a film representing a detailed cross section of tissue structures at a predetermined depth.
tomography
any method that produces images of single tissue planes. In conventional radiology, tomographic images (body-section radiographs) are produced by motion of the x-ray tube and film or by motion of the patient that blurs the image except in a single plane. In reconstruction tomography (CT and PET) the image is produced by a computer program. Called also laminagraphy, planigraphy, body-section technique.
computerized axial tomography
see computed tomography (below).
computed tomography (CT)
a revolutionary radiological imaging modality that uses computer processing to generate an image (CT scan) of the tissue density in a 'slice' about 0.5 inch thick through the patient's body. Called also computerized axial tomography (CAT) and computerized transaxial tomography (CTAT).
Because CT is noninvasive and has high contrast resolution, it has replaced some radiographic procedures using contrast media. However, in some areas the injection of contrast further enhances the image. CT also has a better spatial resolution than scintillation imaging (about 1 mm for CT compared with 15 mm for a scintillation camera).
positron emission tomography (PET)
a combination of computed tomography and scintillation scanning. Natural biochemical substances or drugs tagged with a positron-emitting radioisotope are administered to the subject. After injection, the tagged substance (tracer) is localized in specific tissues like its natural analog. When the isotope decays, it emits a positron, which then annihilates with an electron of a nearby atom, producing two 511 keV gamma rays traveling in opposite directions 180° apart. When the gamma rays trigger a ring of detectors around the subject, the line between the detectors on which the decay occurred is stored in the computer. A computer program (reconstruction algorithm), like those used in computed tomography, produces an image of the distribution of the tracer in the plane of the detector ring.
Most of the isotopes used in PET scanning have a half-life of only 2 to 10 minutes. Therefore, they must be produced by an on-site cyclotron and attached chemically to the tracer and used within minutes. Because of the expense of the scanner and cyclotron, PET is used only in research centers.
ultrasonic tomography
the ultrasonographic visualization of a cross-section of a predetermined plane of the body; see B-mode ultrasonography.
tomography
A radiographic technique for making a detailed X-ray image of a selected plane section of the body while blurring out the images of other planes. The data can be manipulated to represent three-dimensional images of structures.
computed tomography (CT) A radiographic method of viewing a three-dimensional image of a layer of body structures, which is constructed by a computer from a series of plane cross-sectional X-ray images made along an axis. The images indicate the X-ray absorption (called attenuation) of tissues (e.g. bones attenuate most, lungs attenuate least and blood vessels are in between). The X-rays are received by numerous gas or solid-state detectors and computers are used to store, process and manipulate the information received from these detectors. The method yields far better differentiation of tissues than conventional radiography thus providing more precise diagnostic information. Usage includes the detection of orbital fractures, orbital cellulitis, intraorbital calcification, cerebral haemorrhage and orbital tumours. Syn. computerized axial tomography (CAT); CAT scan; CT scan. See glaucoma detection; magnetic resonance imaging; radiology.
confocal scanning laser tomography See confocal scanning laser ophthalmoscope.
optical coherence tomography (OCT) A non-invasive, optical diagnostic imaging technique, which enables in vivo cross-sectional tomographic visualization of internal microstructure in biological systems. OCT is analogous to ultrasound imaging except that it uses light rather than sound, thus achieving approximately 1-100✕ higher image resolution. This is accomplished by using polychromatic (broad bandwidth) or tunable light sources in combination with interferometric techniques to detect depth resolved reflectivity profiles, due to subtle refractive index changes. Several adjacent one-dimensional optical A-scans are combined into two- or three-dimensional tomograms for quantitative analysis of the optic nerve head topography, peripapillary fibre layer thickness, macular retinal thickness, as well as corneal visualization. Quantitative results are compared with an age-matched normative database. OCT can be used for early diagnosis of retinal diseases (e.g. cystoid macular oedema, central serous retinopathy, retinal detachments, macular hole), better understanding of retinal pathogenesis, monitoring of nerve fibre layer thickness and optic nerve head changes in glaucomatous eyes, as well as corneal thickness changes following refractive surgery. Most recent developments enable several 10 thousand measurements per second, allowing three-dimensional retinal images nearly free of motion artifact. In combination with improved resolution this technique has the potential to perform non-invasive optical biopsy of the human retina, i.e. visualization of intraretinal morphology in retinal pathologies approaching the level achieved with histopathology. See glaucoma detection; interference.
positron emission tomography (PET) A neuroimaging technique in which a positron-emitting isotope incorporated into a metabolically active molecule (e.g. fluorodeoxyglucose) is injected intravenously and used as radioactive tracers to generate images of regional cerebral blood flow and glucose consumption contained in the tracers and thus, indirectly brain function. The emitted positron collides with an electron, giving rise to two photons, which strike detectors placed around the head. Tomographic images can be used to construct a three-dimensional image of the relative concentration of the tracer within the brain. PET has been used to study normal and abnormal brain function and to assess tumours, stroke, cortical lesions and also mapping of the visual cortex. See fMRI magnetic resonance imaging; functional neuroimaging.
computed tomography (CT) A radiographic method of viewing a three-dimensional image of a layer of body structures, which is constructed by a computer from a series of plane cross-sectional X-ray images made along an axis. The images indicate the X-ray absorption (called attenuation) of tissues (e.g. bones attenuate most, lungs attenuate least and blood vessels are in between). The X-rays are received by numerous gas or solid-state detectors and computers are used to store, process and manipulate the information received from these detectors. The method yields far better differentiation of tissues than conventional radiography thus providing more precise diagnostic information. Usage includes the detection of orbital fractures, orbital cellulitis, intraorbital calcification, cerebral haemorrhage and orbital tumours. Syn. computerized axial tomography (CAT); CAT scan; CT scan. See glaucoma detection; magnetic resonance imaging; radiology.
confocal scanning laser tomography See confocal scanning laser ophthalmoscope.
optical coherence tomography (OCT) A non-invasive, optical diagnostic imaging technique, which enables in vivo cross-sectional tomographic visualization of internal microstructure in biological systems. OCT is analogous to ultrasound imaging except that it uses light rather than sound, thus achieving approximately 1-100✕ higher image resolution. This is accomplished by using polychromatic (broad bandwidth) or tunable light sources in combination with interferometric techniques to detect depth resolved reflectivity profiles, due to subtle refractive index changes. Several adjacent one-dimensional optical A-scans are combined into two- or three-dimensional tomograms for quantitative analysis of the optic nerve head topography, peripapillary fibre layer thickness, macular retinal thickness, as well as corneal visualization. Quantitative results are compared with an age-matched normative database. OCT can be used for early diagnosis of retinal diseases (e.g. cystoid macular oedema, central serous retinopathy, retinal detachments, macular hole), better understanding of retinal pathogenesis, monitoring of nerve fibre layer thickness and optic nerve head changes in glaucomatous eyes, as well as corneal thickness changes following refractive surgery. Most recent developments enable several 10 thousand measurements per second, allowing three-dimensional retinal images nearly free of motion artifact. In combination with improved resolution this technique has the potential to perform non-invasive optical biopsy of the human retina, i.e. visualization of intraretinal morphology in retinal pathologies approaching the level achieved with histopathology. See glaucoma detection; interference.
positron emission tomography (PET) A neuroimaging technique in which a positron-emitting isotope incorporated into a metabolically active molecule (e.g. fluorodeoxyglucose) is injected intravenously and used as radioactive tracers to generate images of regional cerebral blood flow and glucose consumption contained in the tracers and thus, indirectly brain function. The emitted positron collides with an electron, giving rise to two photons, which strike detectors placed around the head. Tomographic images can be used to construct a three-dimensional image of the relative concentration of the tracer within the brain. PET has been used to study normal and abnormal brain function and to assess tumours, stroke, cortical lesions and also mapping of the visual cortex. See fMRI magnetic resonance imaging; functional neuroimaging.
tomography
Imaging The creation of images at planes located at specific distances from an x-ray beam. See Brain imaging, Computed tomography, Contrast-enhanced electron-beam tomography, Electron beam computed tomography, Focused appendix
computed tomography, High-resolution computed tomography, Nephrotomography, Optical coherence tomography, Positron emission tomography, SPECT tomography, Spiral computed tomography.
How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content.
| ?Page tools | ||
|---|---|---|
|