The CT Scan

The first of the modern brain scanning techniques emerged in the 1970s, as a variation of x-ray technology. It was called the CAT scan. A CAT scan involved rotating an x-ray machine around the axis of a person's body. The series of pictures were like slices through the brain. By combining the information, neuroscientists or physicians can build up a 3-dimensional x-ray of a person's brain. This shows tumors, enlarged ventricles (the fluid-filled cavities of the brain), and other physical deformities in the brain. It does not, however, show which areas are actively processing information.

What is a CAT scan? What does it show? What do the letters stand for? What is it called now, and why?

CAT stands for "computer axial tomography." A tomograph is an x-ray showing a layer of tissue at some specific depth. An axial tomograph is one made by rotating the subject around an axis, which means twirling the subject or twirling the machine. During a CAT scan, the patient lies still and the machine rotates around his or her body. A student who received several CAT scans said they made her feel a bit claustrophobic, because her entire body was inserted into the large machine, which was then rotated around her, taking x-ray images from every angle.

As scanning techniques grew more sophisticated, it was no longer necessary to rotate the X-Ray machine to build up a three-dimensional image. Now an X-Ray machine could sweep over a person (or a mummy, or any other object) and build up a three-dimensional image from the "slices" formed by repeated scans taken from above. The technique is still computerized, and it is still tomography (because it builds up an image from multiple X-Ray slices) but the axial or rotation part of cat scanning is no longer necessary, so the newer technique is called CT scanning.

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