Computed tomography (CT) scanning, also called computerized axial tomography (CAT) scanning, is a medical imaging procedure that uses x-rays to show cross-sectional images of the body.
A CT imaging system produces cross-sectional images or "slices" of areas of the body, like the slices in a loaf of bread. These cross-sectional images are used for a variety of diagnostic and therapeutic purposes.
How a CT system works:

1.A motorized table moves the patient through a circular opening in the CT imaging system.
2.While the patient is inside the opening of the CT imaging system, an medical x-ray source and detector within the housing rotate around the patient. A single rotation takes about 1 second. The x-ray source produces a narrow, fan-shaped beam of x-rays that passes through a section of the patient's body.
3.A detector opposite from the x-ray source records the x-rays passing through the patient's body as a "snapshot" image. Many different "snapshots" (at many angles through the patient) are collected during one complete rotation.
4.For each rotation of the x-ray source and detector, the image data are sent to a computer to reconstruct all of the individual "snapshots" into one or multiple cross-sectional images (slices) of the internal organs and tissues.
Uses
CT can help diagnose or rule out a disease or condition. CT has become recognized as a valuable medical tool, for:
1.Diagnosis of disease, trauma, or abnormality
2.Planning, guiding, and monitoring therapy
Risks and Benefits
As in many aspects of medical x-ray machine, there are risks associated with the use of CT. The main risks associated with CT are:
1.An increased lifetime risk of cancer due to x-ray radiation exposure.
2.Possible allergic reactions or kidney failure due to contrast agent, or “dye” that may be used in some cases to improve visualization.
3.The need for additional follow-up tests after receiving abnormal test results or to monitor the effect of a treatment on disease, such as to monitor a tumor after surgical removal. Some of these tests may be invasive and present additional risks.
Under some rare circumstances of prolonged, high-dose exposure, x-rays can cause other adverse health effects, such as skin reddening (erythema), skin tissue injury, hair loss, cataracts, and potentially, birth defects (if scanning is done during pregnancy).
Radiation exposure is a concern in both adults and children. However, these concerns are greater for children because they are more sensitive to radiation and have a longer life expectancy than adults. As a result, accumulated exposures over a child’s lifetime are more likely to result in an adverse health effect. A child’s smaller size also has an impact on the radiation dose they receive. For example, if a CT scan is performed on a child using the same parameters as those used on an adult, an unnecessarily large dose will be delivered to the child. CT equipment settings (exposure parameters such as, x-ray tube current, slice thickness, or pitch) can be adjusted to reduce dose significantly while maintaining diagnostic image quality.

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