CT scan uses an x-ray beam that passes through the body to produce an image much like a regular X-ray. The Computed Tomography scan x-ray beam spins around you like a saw blade in the circular part of the scanner called the gantry. As you lay on a table that moves in and out of the gantry, the X-ray beam spins around you while you lie on the table that passes you through the spinning x-ray beam.
This abdominal scan illustrates how it works. Imagine slicing a loaf of bread for a sandwich. The knife would represent the x-ray beam that the scanner uses and the loaf of bread would be your body. You can choose how thick or how thin you want the bread to be sliced. You can also choose how many slices you want and where you want to start and end the slices.
Another good example is a spiral cut ham. Suppose you went to the deli section at the grocery store, and asked the butcher for a pound of ham. You would see him put the ham on the meat slicer tray and ask you how thick you want it sliced. The blade on the meat slicer would represent the x-ray beam cutting through the body to produce the images. I promise you, you can not feel an x-ray beam passing through you.
The C.T. Technologist programs a scan by choosing the speed at which the X-ray beam rotates around you, the slice thickness, whether thin or thick and where to start the slices and where to end the slices. We call the accumulation of the slices an acquisition or a data set.
Computed Tomography Scanning often requires more than one acquisition of data or several data sets depending on the need.
The "a" in cat scan has been dropped and is now known as ct scan.