All light and radio waves belong to the electromagnetic spectrum and are all considered different types of electromagnetic waves, including:

Microwaves and infrared bands whose waves are longer than those of visible light (between radio and the visible).

UV, EUV, x-rays, and g-rays (gamma rays) with shorter wavelengths.

The electromagnetic nature of x-rays became evident when it was found that crystals bent their path in the same way as gratings bent visible light: the orderly rows of atoms in the crystal acted like the grooves of a grating.

Medical X-Rays

X-rays are capable of penetrating some thickness of matter. Medical x-rays are produced by letting a stream of fast electrons come to a sudden stop at a metal plate; it is believed that x-rays emitted by the Sun or stars also come from fast electrons.

The images produced by x-rays are due to the different absorption rates of different tissues. Calcium in bones absorbs x-rays the most, so bones look white on a film recording of the x-ray image, called a radiograph. Fat and other soft tissues absorb less and look gray. Air absorbs the least, so lungs look black on a radiograph.

Wilhelm Conrad Röntgen Takes the First X-Ray

On 8 Nov 1895, Wilhelm Conrad Röntgen (accidentally) discovered an image cast from his cathode ray generator, projected far beyond the possible range of the cathode rays (now known as an electron beam). Further investigation showed that the rays were generated at the point of contact of the cathode ray beam on the interior of the vacuum tube, that they were not deflected by magnetic fields, and they penetrated many kinds of matter.

A week after his discovery, Rontgen took an x-ray photograph of his wife's hand which clearly revealed her wedding ring and her bones. The photograph electrified the general public and aroused great scientific interest in the new form of radiation. Röntgen named the new form of radiation x-radiation (X standing for "Unknown"). Hence the term x-rays (also referred to as Röntgen rays, though this term is unusual outside of Germany).

William Coolidge & X-Ray Tube

William Coolidge invented the X-ray tube popularly called the Coolidge tube. His invention revolutionized the generation of X-rays and is the model upon which all X-ray tubes for medical applications are based.

Coolidge Invents Ductile Tungsten

A breakthrough in tungsten applications was made by W. D. Coolidge in 1903. Coolidge succeeded in preparing a ductile tungsten wire by doping tungsten oxide before reduction. The resulting metal powder was pressed, sintered and forged to thin rods. A Very thin wire was then drawn from these rods. This was the beginning of tungsten powder metallurgy, which was instrumental in the rapid development of the lamp industry.

X-Rays and the Development of the CAT-Scan

A computed tomography scan or CAT-scan uses x-rays to create images of the body. However, a radiograph (x-ray) and a CAT-scan show different types of information. An x-ray is a two-dimensional picture and a CAT-scan is three-dimensional. By imaging and looking at several three-dimensional slices of a body (like slices of bread) a doctor could not only tell if a tumor is present but roughly how deep it is in the body. These slices are no less than 3-5 mm apart. The newer spiral (also called helical) CAT-scan takes continuous pictures of the body in a spiral motion so that there are no gaps in the pictures collected.

A CAT-scan can be three dimensional because the information about how much of the X-rays are passing through a body is collected not just on a flat piece of film, but on a computer. The data from a CAT-scan can then be computer-enhanced to be more sensitive than a plain radiograph.

Robert Ledley was the inventor of CAT-scans and was granted patent #3,922,552 on November 25th in 1975 for "diagnostic x-ray systems" also known as CAT-scans.