Tomography for Dummies

As stated in our brief introduction on the homepage, tomography, most commonly known as computed tomography (CT), is simply a mathematical process of taking a 3-D object and representing it through a series of 2-D "slices" of the object. These 2-D "slices" or images are most often created by passing x-rays "through" the object and collecting the 2-D projections created from the x-rays. These projections of the 3-D object are taken from all different sides of the object - each different angle we take the projections at tells us something different about what the inside of this 3-D object looks like. After taking enough projections and gathering enough information about the objects "contents" we can combine these projections and reconstruct what a "slice" of the object at the place where we took our projections would look like.

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Multimedia Demonstration

The animated clip to the left shows how a CT machine reconstructs a "slice" of something, in this case the human head. The clip begins showing just one projection of the image, a collection of horizontal lines - this can be thought of as representing the various densities of the head (similar to a shadow - where the brain is denser there are more "shadows"). As more projections are made at different angles, represented by the animation twisting around, and they are combined together, we can start to see the form of the human head reconstructed from all of these projections.
Once the image has been completed twisted around we can recognize the image, but it is very fuzzy. In order to correct this problem, we must filter the image to remove the unwanted "noise." This final step is shown in the movie clip where we finally see the image become sharp - we have now created a "slice" of the human head without any mess.