X-ray beams are generated in a vacuum x-ray tube. In the x-ray tube are a negatively charged cathode and a positively charged anode. The cathode generally consists of a tungsten spiral. Passing an electrical current through the cathode will cause powerful heating (> 2200°C) of the spiral. The heating causes emission of electrons. The potential difference between the anode and cathode (= tube charge) will cause the electrons to shoot towards the positively charged anode (= focus/target). As the electron flow (= tube current) in the anode decelerates, the kinetic energy of the electrons is converted into x-rays (fig. 1).
Figure 1. X-rays are generated in the x-ray tube. The x-ray beam passes through the body part and hits a phosphorus plate/detector.
The tube charge is expressed in kilovolts (kV) and the tube current is expressed in milliampere (mA).