tomography
(tō-mog'ră-fē 
)
[tomo- + -graphy]
A radiographic technique that selects a level in the body and blurs out structures above and below that plane, leaving a clear image of the selected anatomy. This is accomplished by moving the x-ray tube in the opposite direction from the imaging device around a stationary fulcrum defining the plane of interest. Tube movements can be linear, curvilinear, circular, elliptical, figure eight, hypocycloidal, or trispiral. With the exception of renal tomography most tomographic procedures have been replaced by computed tomography (CT). SYN: body section radiography; body section roentgenography.
ABBR: CAT
SEE: computed tomography.
ABBR: CT
A computerized x-ray scanning system that produces a sectional anatomic image. It is achieved by digital processing of x-ray attenuation coefficients from a 360° wedge scan of ionizing radiation. There is considerable use of data from the attenuation coefficients in diagnosis. Computed tomography is colloquially called a cat scan.
CT scans expose patients to radiation on the order of 10 milliSieverts (mSv) per scan. Educational materials about the potential risks and benefits of scanning should be provided to patients to ensure that scans are performed safely and carefully.ABBR: CAT
SEE: computed tomography.
electrical impedance t.Cross-sectional body imaging that reconstructs pictures of internal organs based on measurements of their electrical activity as detected by electrodes placed on the surface of the body.
electron-beam t.Ultrafast computed tomography
ABBR: FBCT
An examination from head to toe of the body with computed tomographic imaging, promoted as a screening test for cancer and other illnesses. The test exposes patients to high levels of radiation, reveals more false positive findings than true positives, and is expensive.ABBR: HRT
A kind of laser scanning system that produces three-dimensional images of the posterior segment of the eye. It is used to diagnose and treat glaucoma.helical computed t.Computed tomographic (CT) images that are obtained as the CT table moves continuously during a single, held breath. Detailed evaluation of dynamic internal features is feasible with this technique. SYN: spiral computed tomography.
ABBR: OCT
A radiographical method used to obtain high-resolution cross-sectional images of tissues and their defects, e.g., of the structures of the eye.ABBR: PET
Imaging of body parts by using positron-emitting radionuclides. By using several different radionuclides, researchers can measure regional cerebral blood flow, blood volume, oxygen uptake, and glucose transport and metabolism, and can locate neurotransmitter receptors. PET has been used with fludeoxyglucose F 18 to identify and localize regional lymph node metastases and to help assess response to therapy.The images produced by PET are in colors that indicate the degree of metabolism or blood flow. The highest rates appear red, those lower appear yellow, then green, and the lowest rates appear blue. The images in various disease states may then be compared to those of normal subjects. Three- and four-dimensional reconstructions are often achieved through the use of computed tomography (CT) with the same machine.
SEE: illus.
ABBR: QCT
A method for determining the bone mineral density of a three-dimensional bony specimen, e.g., in the vertebral bodies or the forearms. It is used in the diagnosis of osteopenia and osteoporosis.single photon emission computed t.
ABBR: SPET, SPECT
A medical imaging method for reconstructing sectional images of radiotracer distributions.SEE: nuclear medicine scanning test; positron emission tomography.
spiral computed t.Helical computed tomography.
ultrafast computed t.Computed tomographic scanning that produces images by rotating the x-ray beam at targets placed around a patient, instead of moving a patient on a gantry through the scanner. The technique minimizes patient movement artifacts and decreases scanning times to about 50 to 100 msec. It is capable of providing good resolution of vascular structures, such as the aorta and the coronary arteries. SYN: electron-beam tomography.
xenon-enhanced computed t.Computed tomographic scanning that uses the inert gas xenon to improve the visual distinction between healthy and abnormal tissues, esp. to visualize blood flow to different regions of the brain in stroke.