X-rays
CAT scans work by using X-rays to image the body. X-rays are able to get a picture of the inside of the body because different kinds of tissue absorb X-ray beams differently. The X-ray beams are generated externally and directed at the body. The more solid the tissue, the more of the X-ray beams it absorbs. Bones absorb almost all of the X-ray beams; dense tissue (such as muscle) absorb a moderate amount of the radiation and air-filled spaces (like the lungs) absorb almost no radiation. X-ray beams that are not absorbed pass through the body and are absorbed by a detector. A standard X-ray gives a two-dimensional view of the body from one angle.
CAT Scan Principles
Although CAT scans also use X-ray beams to make an image of the body, they do so in a more complex way. With a CAT scan, X-rays are directed at the body from different angles, which gives many different images and provides much more information than a standard X-ray. With a CAT scan, a computer takes all of these different images and then combines them together into a series of cross-sections. In essence, a CAT scan takes many different images of the body and turns them into little slices of the body. Sometimes patients getting a CAT scan are injected with special dyes that make some tissues easier to see.
CAT Scan Procedure
When a patient gets a CAT scan, he initially lies flat (typically on his back) on a small mobile table. The table then moves her into the CAT machine, which has a cylindrical opening. Once inside the machine, an X-ray generator and detector moves around the patient and takes multiple images of the patient. Typically, the generator/detector combo rotates around the patient between 10 and 50 times during the course of the exam. Sometimes the patient is asked to hold her breath to avoid blurring the images. The images are then sent to a computer, which analyzes the data and displays it as a series of cross-sections that a doctor can examine.
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