What Is Tomography? - Definition & History

Instructor: Meghan Greenwood

Meghan has taught undergraduate and graduate level science courses and has a PhD in Immunology.

This lesson will define tomography and explain the various techniques used for the process. It will also give a brief overview of the history of the technology.

What is Tomography?

Think of the last time you or a family member was injured. You likely went to the hospital, and they may have checked the area of injury with an imaging procedure. Maybe it was an X-ray machine, which delivers a beam of light into the body, allowing for visualization of organs that are not able to be seen by the naked eye (that is, without cutting into the body and opening up the skin). About 40 years ago, technology advanced beyond the single plane images displayed on a piece of film and is now able to produce a cross-sectional image of your organs, bones and tissues.

An example X-ray image of a human skull.
X-ray of skull

Tomography is a visualization process that produces an image of what's inside a tissue. Imagine a loaf of bread. When you cut into the loaf, you are then able to view what was once hidden by an outer layer of crust -- the slice, or cross-section, gives you the ability to see both sides of the piece of bread. The same idea applies for tomography. Although the image generated is still two-dimensional, doctors are now able to see into tissues.

Even more informative is the ability of tomography to generate images of multiple slices of the tissue, from one end to the other. Think again of the bread example. Say you turn the loaf of bread vertically and begin slicing it from the top down to the bottom. Each slice may be a little different. Perhaps one of the slices reveals a hole in the bread or another contains a green mold. The capability of imaging serial slices allows the doctor to see through the whole tissue, one slice at a time, in an effort to not miss anything that may indicate injury or disease.

An example tomography of the brain, with serial sections from the top of the skull to the base of the stem.
Brain tomography

Types of Tomography

Tomography is a general term for section imaging. Many different procedures utilize the process. Two of the more common techniques are CT scans and MRIs. A CT scan, or computed tomography scan, is a computerized X-ray technique used to generate the serial sections. CT scans can provide visualization of almost every part of the body and are most often used to detect injury or disease, such as internal bleeding or tumor growth.

In contrast, MRIs do not use X-rays, but instead magnetic fields to produce serial images of the body's internal organs. Like CT scans, they are often used to help diagnose injury and disease (i.e. detecting a joint injury or uterine cyst), but because an MRI does not use X-rays, there is a reduced risk of exposure to the patient. Determining which type of tomography procedure you should undergo depends mainly on the area of the body affected and what the reason is for the test. For example, CT scans are best for detecting lung cancer, whereas MRIs are better for diagnosing spinal cord injuries.

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