A CAT scan (computer assisted tomography or computed axial  tomography or computed tomography, CT) is a three-dimensional (3D)  image reconstructed from a series of two-dimensional X-ray images.  Compared with a conventional X-ray image, a CAT scan provides better  resolution, which helps identify the position, size and shape of  tumors, among other medical applications.

Cormack won the Nobel Prize in medicine in 1979 for discovering the mathematical formulas that allow scientists to  reconstruct an object's cross section from a series of two-dimensional  X-ray images. (Co-winner Godfrey Hounsfield constructed the first CAT  scan system used in medical care.)

Other imaging methods, such as magnetic resonance imaging ,  frequently are used in medicine today, but computed tomography is still  popular among scientists. Structural biologists use cryo-electron  tomography to reconstruct 3D images of proteins from multiple 2D images  taken using an electron microscope. This technique is similar to a CAT  scan, except the specimen is frozen and repeatedly tilted to acquire  images from different angles (in a medical CAT scan, the patient lies  still, at room temperature, while the X-ray source rotates around the  patient).

Researchers also use a variation of the CAT scan to examine fossils.  High-resolution X-ray CT can resolve much finer details than medical  CAT scans, probably because radiation exposure is not an issue with  animal remains.

My favorite use of CT scanning? Rather than disassembling a vintage  guitar to see how it was built, scientists used CT scans to determine  how the instrument's bracing was assembled . The Gretsch model 6120 was manufactured with unique bracing from 1959-1961. Once the CT scan  revealed the instrument's exact measurements, guitar makers were able  to recreate the unique bracing.