An x-ray tube functions as a specific energy converter, receiving the electrical energy and converting it into two other forms of energy: x-radiation and heat. Heat is considered the undesirable product of this conversion process; therefore x-radiation is created by taking the energy from the electrons and converting it into photons. This very specific energy conversion takes place in the x-ray tube.

Construction of the x-ray tube

The x-ray tube contains two principal elements:

  1. cathode: provides a source of electrons
  2. anode (or anticathode): acts as the target for electrons and releases x-rays

Additional components include:

  • expansion bellows (provide space for oil to expand)
  • tube envelope (evacuated)
  • tube housing
  • cooling dielectric oil
  • rotor
  • induction stator
  • tube window: usually made from beryllium, not glass

The cathode and anode are contained in the envelope, which provides vacuum, support and electrical insulation. The envelope is most often made from glass, although some tubes contain envelopes formed from ceramic or even metal. For some demanding application such as dual energy CT rotating envelope tubes (RET) are used. Unlike conventional x-ray tubes in RETs not only the anode, but the entire vacuum tube rotates, furthermore, the anode is in direct contact with the liquid coolant, resulting in improved heat conduction and increased performance 7

The energy used for this process is provided from the generator, connected by an electrical circuit connected to the system. The generator also needs to convert the alternating current (AC), from the power supply, into direct current (DC), as needed by the x-ray tube.

The quality and the quantity of the x-radiation are controlled by adjusting the electrical parameters (kV – voltage or the potential applied to the tube, mA – current that flows through the tube) and exposure time, usually a fraction of a second.

To summarize, x-rays are produced in a standard way: by accelerating electrons with a high voltage and allowing them to collide with the focal spot. X-rays are produced when the electrons are suddenly decelerated upon collision with the metal target. These x-rays are called “braking radiation” (bremsstrahlung). If the electrons have high energy, they can expel an electron out of the atomic shell of the bombarded atom. Electrons from a higher energy level fill the place of the expelled electron, emitting x-ray photons with quantized (precise) energies, determined by the respective electron energy levels. The x-rays produced in this way are called “characteristic x-rays”.

Imaging technology

Article information

rID: 8177
Synonyms or Alternate Spellings:
  • CT x-ray tube
  • X-ray tubes

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Cases and figures

  • Figure 1: x-ray tube diagram
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  • Figure 2: x-ray tube diagram
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