X-rays are electromagnetic waves of short wavelength, 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. Both light and radio waves belong to the electromagnetic spectrum, the range containing all different electromagnetic waves. Over the years scientists and engineers have created EM waves of other frequencies--microwaves and various IR bands whose waves are longer than those of visible light (between radio and the visible), and 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.

Left: Wilhelm Röntgen (Roentgen)

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.

Right: Mrs. Röntgen's hand, the first X-ray picture of the human body ever taken.

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 as Röntgen rays, though this term is unusual outside of Germany).

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.

Some information and all photos courtesy of NASA

Discovery of the X-Ray
An historical overview of the discovery of the X-Ray.

Original patent drawing of the first CAT-scan

Robert S. Ledley - CAT-Scans
Diagnostic X-Ray Systems -  CAT-Scans
Robert S. Ledley was granted patent #3,922,552 on November 25th in 1975 for a "diagnostic X-ray systems" also known as CAT-Scans.

A computed tomography scan (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.

William D. Coolidge
X-Ray Tube
William D. Coolidge invented the X-ray tube - popularly called the 'Coolidge tube.'

William D. Coolidge
William D. Coolidge invented the X-ray tube - Invention Dimension.

Other inventions of Coolidge: invention of 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. 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 - International Tungsten Industry Association (ITIA)

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