CT scan, CAT scan

CT or CAT scan stands for Computed Axial Tomography. CT scans are a specialized form of xray imaging. The now-familiar scanner consists of a ring device that surrounds the patient which contains a moveable xray source with an electronic xray sensor on exactly the opposite side of the circle. Very low level xrays are sent through the body from the source to the sensor from every angle of orientation around the patient. A computer mathematically calculates the xray density of each of several million tiny locations in a given "slice" through the body and then displays the resulting image for interpretation on a computer screen or prints it to xray film. The amount of x-radiation delivered to the patient can be significant, especially if the scanner is not ordinarily used for children and the "tube current" is not adjusted lower for pediatric patients.

Modern CT scanners are often enhanced by means of computer software programs to allow the construction of three-dimensional views as well. CT is not always the best imaging choice for a given clinical situation; MRI is better for soft tissue detail, and often ultrasound imaging, while not as detailed, is so much easier and cheaper to do, as well as avoiding radiation exposure altogether, that it is the preferred imaging method.

Computed - obviously
Axial - referring to the long axis of the body, perpendicular to which the "slices" are taken
Tomography - from tomo -> slice or cross section

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