"Computed Axial Tomography" is the process of using computers to generate a
three-dimensional image from flat (i.e, two-dimensional) x-ray pictures, one
slice at a time...
What do you mean by "slice"?
There's a lot of complexity on the inside that you can't guess from the
outside, bits of fruit and nuts all over the place. How could you go about
exploring the inside of a whole fruitcake?
Oh, I see what you mean now. If I sliced it up I could look at each slice and
get an overall picture.
OK, but we just said that CAT scans are useful because x-ray machines only
take flat, two dimensional pictures and we want three dimensional pictures. So
why is the process of imaging the flat "slices" difficult? Isn't making flat
pictures what x-ray machines do?
The problem is that the flat x-ray we get is of the whole thing. It would be
like crushing our fruitcake under a steam roller and saying, "There! Now we
can see everything!" But we would have lost all the information about how
"deep" the pieces of fruit and nuts were.
So how do we take x-rays of a slice in the middle? We could just turn the
fruitcake sideways, but then all the other slices would get in the way. How do
we take x-rays of only one slice?
Very good! That's exactly the right question to ask. Let's explore that.