4. X-ray sources and generators

4.1 X-ray source operation

The X-rays used in medical imaging are produced in Coolidge tubes (named after their inventor in 1913, a researcher at GENERAL ELECTRIC's Schenectady laboratory) powered by a high-voltage generator, usually remote. They provide the braking radiation (bremsstrahlung) for a beam of high-energy electrons, which strike a metal target in a vacuum envelope. This target is tilted by an angle α of between 7 and 15°, so that most of the X-ray photons created radiate towards the tube window, and the target is properly cooled: the greater the tilt, the greater the area of impact of the electrons on the target (figure