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A computed axial tomography scan or CT Scan (also CAT Scan) is a medical imaging technology that uses finely focused X-rays together with a detector rather than photographic film combined with computer imaging technology to create detailed three-dimensional images of interior body tissue, including soft tissue. It is primarily used to detect and locate structures within the body that cannot be located by other forms of radiological investigation.

Traditional X-rays suffer from their inability to give any perception of depth to the physician. This is because the X-ray can only picture the average density of any tissue in front of the X-ray film. A CT Scan gets around this limitation in three ways:

- Instead of using a broad beam of X-rays, a CT Scan uses a very narrowly focused beam of X-rays that can only penetrate straight through the body in a straight line to the detector.

- The X-ray source is rotated around the body so that the X-rays pass through the entire structure in both directions.

- A computer is used to reconstruct the intensity of the X-rays into an image showing the density of any point of the plane through which the X-rays passed.

As such, the CT Scan can produce images that appear as "slices" of tissues, showing the exact location of structures within otherwise solid tissues. As such, it is much better than other techniques for detecting bleeding within the skull or tumors. Another advantage is that CT Scans can be performed to essentially ignore any structure the physician isn't interested in. For example, it can be focused on structures of the brain rather than just scanning the entire head.

The main problem with a CT Scan is the exposure to radiation. It exposes a patient to far more radiation than a conventional X-Ray. Although it is not a problem for most patients, it must be avoided for persons particularly sensitive to radiation, such as pregnant mothers.

X-ray computed tomography at Wikipedia