Tomography is a branch of imaging which produces an image called a tomogram which shows a single plane of an object in very specific detail. Many people think of tomography in terms of medical imaging, which is used to create a cross section of the body to reveal underlying medical conditions. Other branches of science also utilize tomography, including biology, geology, oceanography, archeology, and materials science. The technique has been used since the mid twentieth century, although the technology for producing tomograms is constantly improving.
By creating a tomogram, a scientist can look into something without actively cutting it open. In a field like archeology, this ensures that the integrity of specimens is respectfully preserved while they are studied. In medicine, tomography is less invasive than exploratory surgery, and it can provide an excellent idea about what is going on inside the patient for medical providers. Geologists use it to look at cross sections of rock and other material, and the technique even pops up in some high-tech criminal labs so that evidence can be analyzed without being destroyed.
The math behind tomography is quite complex. Essentially, rays are passed through the object being imaged, and the rays, or the tomograph machine are moved during the imaging process to blur out other planes and pull one cross section into sharp detail. Usually the specimen is kept still, and keeping still is an important direction in medical imaging to ensure crisp images. Unfortunately for patients, the medical devices used to create tomographic images can be very noisy and cramped, making the direction to hold still very uncomfortable.
A number of different rays are used in tomography, including X-rays, gamma rays, ultrasound, magnetic resonance, and others. Once images of the object in question have been acquired, they are run through a computer program which cleans up the images and creates a clear cross-section. Some computer reconstruction programs can also create a three dimensional image of the object which can be manipulated to get more information about its internal workings.
As with other imaging techniques which bombard objects with energy, tomography can be dangerous. People who regularly perform tomographic imaging usually shield themselves by standing behind a barrier or wearing special gear which is designed to resist harmful radiation. For patients, a certain amount of lifetime exposure is somewhat inevitable, but it does become a concern when a patient is subjected to repeated diagnostic imaging in an attempt to get to the bottom of a medical problem.