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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.
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.
CATcomputerized axial tomography.
CATA 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.
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.
catFelis 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 medicine.bu.edu/dshapiro/zoocat.htm
- Some individuals are highly allergic to cats, which is attributed to the Fel dl antigen, see there .
tomography(to-mog'ra-fe) [ tomo- + -graphy]
computed axial tomographyAbbreviation: CAT
See: computed tomography
computed tomographyAbbreviation: CT
CAUTION!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 tomographyAbbreviation: CAT
See: computed tomography
electrical impedance tomography
electron-beam tomographyUltrafast computed tomography
full body computed tomographyAbbreviation: FBCT
CAUTION!The test exposes patients to high levels of radiation, reveals more false positive findings than true positives, and is expensive.
Heidelberg retinal tomographyAbbreviation: HRT
helical computed tomography
optical coherence tomographyAbbreviation: OCT
positron emission tomographyAbbreviation: PET
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 tomographyAbbreviation: QCT
single photon emission computed tomographyAbbreviation: SPET, SPECT
spiral computed tomographyHelical computed tomography.
ultrafast computed tomography
xenon-enhanced computed tomography
CATAbbrev. for computerized axial tomography (CT SCANNING).
CT or CAT
Patient discussion about CAT
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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...