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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.
computed tomography (CT) (computerized axial tomography (CAT)) a radiologic imaging modality that uses computer processing to generate an image (CAT scan) of the tissue density in a “slice” as thin as 1 to 10 mm in thickness through the patient's body. These images are spaced at intervals of 0.5 to 1 cm. Cross-sectional anatomy can be reconstructed in several planes without exposing the patient to additional radiation.

Since its introduction in 1972, the use of this modality has grown rapidly. Because it is noninvasive and has high contrast resolution, it has replaced some radiographic procedures using contrast media. It also has a better spatial resolution than scintillation imaging (about 1 mm for CAT compared to 15 mm for a scintillation camera).

A CAT scan is divided into a square matrix of pixels (picture elements). The newer CAT scanners use a high resolution matrix with 256 × 256 or 512 × 512 pixels. The region of the tissue slice corresponding to a pixel has a cross-sectional area of 1 × 1 mm to 2 × 2 mm; because of the thickness of the slice, it has a finite height and is therefore referred to as a voxel (volume element).

The actual measurements made by the scanner are the x-ray attenuations along thousands of rays traversing the slice at all angles. The attenuation value for a ray is the sum of the values for all of the voxels it passes through. A computer program called a reconstruction algorithm can solve the problem of assigning attenuation values for all the pixels that add up to the measured values along each ray.

The attenuation values are converted to CAT numbers by subtracting the attenuation value of water and multiplying by an arbitrary coefficient to produce values ranging from −1000 for air to +1000 for compact bone with water as 0. CT numbers are sometimes expressed in Hounsfield units, named after Godfrey Hounsfield, the inventor of the CT scanner; Hounsfield and Allan Cormack were co-winners of the Nobel Prize in physiology or medicine in 1979 for the development of computerized axial tomography.
Computed tomography. Relative position of the x-ray tube, patient, and detectors in a fourth generation CT unit.
electron beam computed tomography (EBCT) ultrafast computed tomography done with a scanner in which the patient is surrounded by a large circular anode that emits x-rays as the electron beam is guided around it.
extended narrow tomography tomography involving an increase in amplitude and increase in exposure angle resulting in greater thinness of the cut for examination.
linear tomography tomography in which the tube and film move in the same direction.
narrow angle tomography a type of tomography that results in thicker sections for examination.
pluridirectional tomography tomography in which there is a great deal of movement in a variety of directions.
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 by injection; the tagged substance (tracer) then becomes localized in specific tissues like its natural analogue. 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 degrees 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. However, PET is important because it provides information that cannot be obtained by other means. By labeling the blood with 11C-carbon monoxide, which binds to hemoglobin, images can be obtained showing the regional perfusion of an organ in multiple planes. By using labeled metabolites, images can be obtained showing metabolic activity of an organ. 15O-oxygen and 11C-glucose have been used for brain imaging and 11C-palmitate for heart imaging. 81Rb, which is distributed like potassium, is also used for heart imaging. By using labeled neurotransmitters, hormones, and drugs the distribution of receptors for these substances in the brain and other organs can be mapped.
single-photon emission computed tomography (SPECT) a type of tomography in which gamma photon–emitting radionuclides are administered to patients and then detected by one or more gamma cameras rotated around the patient. From the series of two-dimensional images produced, a three-dimensional image can be created by computer reconstruction. The technique improves resolution of, and decreases interference by, overlapping organs. It is used particularly for assessment of cardiac disease, stroke, and liver disease; for staging of cancer; and to diagnose physical abnormalities through evaluation of function.
ultrasonic tomography the ultrasonographic visualization of a cross-section of a predetermined plane of the body; see B-mode ultrasonography.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


Abbreviation for chloramphenicol acetyl transferase; obsolete abbreviation for computerized axial tomography (CT).
Farlex Partner Medical Dictionary © Farlex 2012


1. clear-air turbulence
2. computerized axial tomography


a. A small domesticated carnivorous mammal (Felis catus), kept as a pet and as catcher of vermin, and existing in a variety of breeds.
b. Any of various other carnivorous mammals of the family Felidae, including the lion, tiger, leopard, and lynx.
c. The fur of a domestic cat.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A gene on chromosome 11p13 that encodes catalase, an enzyme which plays a central role in the body’s defence against oxidative stress, converting the reactive oxygen species hydrogen peroxide (H2O2) to water and oxygen, thereby mitigating H2O2’s toxic effects.

Molecular pathology
Defects in CAT cause acatalasemia. Oxidative stress may play a role in the development of chronic or late-onset diseases—e.g., diabetes, asthma, Alzheimer's disease, systemic lupus erythematosus, rheumatoid arthritis and cancer.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


1. Catalase.
2. Catalyst.
3. Catecholamine.
4. Chloramphenicol acetyl transferase, a 'reporter' gene.
5. Choline acetyl transferase.
6. Cholesterol acyl transferase.
7. Computerized axial tomography, see there.


Felis catus A mammal of medical interest that is a model for some human diseases, eg, dermatosparasix, and a vector for bacteria, fungi, and parasites
Cats, impact on medicine
Model systems
-human diseases, eg dermatosparasix, a defect in converting type I procollagen to collagen; mannosidosis–affects shorthair cats; Niemann-Pick disease, type I–affects Siamese cats
Vectors for disease
  • Bacteria Bartonella (Rochalimaea) henselae, Bergeyella (Weeksella) zoohelcum, Brucella suis—anthrax, Campylobacter jejuni, Capnocytophaga canimorsus, CDC group NO-1, Chlamydia psittaci–feline strain, Dipylidium caninum, Francisella tularensis, Neisseria canis, Pasteurella multocida, Q-fever, Rickettsia felis, salmonellosis, Yersinia pestis–plague, Yersinia pseudotuberculosis
  • Fungi, eg Microsporum canis–dermatophytosis, Sporothrix schenckii
  • Parasites, eg Ancylostoma braziliense, A caninum, Brugia pahangi*, Clonorchis sinensis, Cryptosporidium, cutaneous larva migrans, Dipylidium caninum, Dracunculiasis medinensis*, Echinococcus vogeli, E multilocularis, Gnathostoma spinigerum, Isospora belli, Leptospira spp–leptospirosis, Opistorchis felineus, Sarcoptes scabiei–scabies, Toxoplasma gondii, Trypanosoma cruzi*, Trichinosis, visceral larva migrans, Wuchereria bancrofti. See Cat scratch disease
  • .
  • Viruses Cowpox, poxvirus, rabies
Some individuals are highly allergic to cats, which is attributed to the Fel dl antigen, see there
*Parasites that have part of their life cycle in humans
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


Abbreviation for chloramphenicol acetyl transferase;
[obsolete] computed axial tomography.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(to-mog'ra-fe) [ 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). Synonym: body section radiography; body section roentgenography

computed axial tomography

Abbreviation: CAT
See: computed tomography

computed tomography

Abbreviation: 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 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.

computerized axial tomography

Abbreviation: CAT
See: computed tomography

electrical impedance tomography

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 tomography

Ultrafast computed tomography

full body computed tomography

Abbreviation: 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.

Heidelberg retinal tomography

Abbreviation: HRT
A confocal 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 tomography

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.
Synonym: spiral computed tomography

optical coherence tomography

Abbreviation: 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.

panoramic tomography

Enlarge picture
Enlarge picture

positron emission tomography

Abbreviation: PET
Reconstruction of brain sections 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: illustration


quantitative computed tomography

Abbreviation: 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 tomography

Abbreviation: SPET, SPECT
A medical imaging method for reconstructing sectional images of radiotracer distributions.
See: nuclear medicine scanning test; positron emission tomography

spiral computed tomography

Helical computed tomography.

ultrafast computed tomography

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. Synonym: electron-beam tomography

xenon-enhanced computed tomography

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.
Medical Dictionary, © 2009 Farlex and Partners


Abbrev. for computerized axial tomography (CT SCANNING).
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


Computed tomography, a radiologic imaging that uses computer processing to generate an image of tissue density in slices through the patient's body.
Mentioned in: Histiocytosis X
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

Patient discussion about CAT

Q. Any one used or know anything about cats claw? What you think about this site ?

A. There's some info here:

To your health...

Q. Can it be that I stopped being allergic to cats? is it a miracle? I was allergic to cats in my childhood, and yesterday a friend cat jumped on me and nothing happened.


Q. i LOVE cats! but whenever I get near them I start sneezing like crazy Is there something I can take that will prevent this allergic reaction? cause I'm just dying to get a fluffy little kitty...

A. i know a guy who's going through an anti-allergy treatment (for the last year and a half). he is going every month or so and get a shot. i think this is the treatment:

More discussions about CAT
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References in periodicals archive ?
In addition to tissues from the contemporary outbreak, we analyzed DNA from 3 historically infected (2002-2004; FFWCC) FeLV-infected Florida panthers (FP115, FP122, and FP132), and 4 domestic cats from Florida (x1608, x1613, x2653, and x2655) collected during 2008-2018 for FeLV genomes (Table 1).
Dr Ritchie said: "Several cat species have been cloned using the domestic cat, just like the wolf has using dog eggs.
"If someone has a domestic cat that they care for, feed, neuter and vaccinate and it gets attacked in their back garden by a wild cat that has feline AIDS, then it is going to get contract the disease.
A 2012 systematic review reported that free-ranging domestic cats are probably responsible for the greatest percentage of bird and mammal deaths (13).
The study also revealed that 30 percent of the wildlife killed by domestic cats was eaten immediately but 49 percent was simply left to rot where it died.
DOMESTIC cats have developed subtle ways of psyching out their owners to get what they want, a scientific study has shown.
The Ethiopian Wildlife Service was called in to snare the wild cat after it had eaten several domestic cats and rabbits on the 67-acre forested estate in the capital, Addis Ababa.
Laura Peterson's dark yet beautiful color illustrations add a dramatic touch to this simple story, which is grounded in the very real tragedy that feral cats have brought to the land of Australia--after their introduction by Australian settlers, many domestic cats and other animals have turned feral, and since Australia has no natural predator like them, they have exacted a devastating toll on the continent's wildlife, even rendering some species extinct.
WITH estimates of up to nine million domestic cats living in the UK, feline friends can often turn out to be more like foes for gardeners.
The fall could lead to outbreaks of diseases among domestic cats, dogs and rabbits.
NINETY per cent of domestic cats need to be neutered to avoid the feline population spiralling out of control, RSPCA Cymru Wales has warned.
The streets are full of hungry domestic cats, thrown out of their homes by bored Maltese or incontinent, retired British sunseekers.

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