What is Bremsstrahlung radiation?
Bremsstrahlung radiation is produced when a high-speed electron is decelerated or deflected by the electric field of an atomic nucleus. As the electron loses kinetic energy during this interaction, the lost energy is emitted as an X-ray photon.
Bremsstrahlung radiation is produced when electrons are decelerated by atomic nuclei, generating a continuous spectrum of X-ray photon energies.
Because the amount of energy lost during each interaction can vary continuously, Bremsstrahlung radiation produces a continuous spectrum of photon energies. It is the dominant mechanism of X-ray production in diagnostic radiology.
Understanding the physics
When electrons accelerated across the X-ray tube strike the anode target, they interact with the atoms of the target material. In Bremsstrahlung interactions, the incoming electron passes close to the positively charged nucleus of a target atom.
The strong electrostatic attraction between the negatively charged electron and the positively charged nucleus causes the electron to change direction and slow down. This rapid deceleration results in the emission of electromagnetic radiation in the form of an X-ray photon.
The energy of the emitted photon is equal to the loss of kinetic energy of the electron during the interaction.
If the electron passes relatively far from the nucleus, it loses only a small amount of energy and produces a low-energy photon. If it passes very close to the nucleus, a large fraction of its kinetic energy may be lost in a single interaction, producing a high-energy photon. In the extreme case where the electron loses all of its kinetic energy, the emitted photon will have the maximum possible energy, equal to the energy the electron gained from the applied tube voltage:
E(max) = e x kVp
Because the degree of electron deceleration varies from interaction to interaction, the photon energies produced form a continuous range from near zero up to this maximum value. This continuous distribution is what forms the Bremsstrahlung X-ray spectrum.
The probability of Bremsstrahlung production increases with higher electron energy and with higher atomic number of the target material. This is one reason tungsten, with a high atomic number (Z = 74), is commonly used in X-ray tube targets.
Where this matters clinically
Bremsstrahlung radiation accounts for the majority of photons in diagnostic X-ray beams. It therefore largely determines:
The shape of the X-ray spectrum
Beam penetration
Patient radiation dose
Image contrast
Adjusting kVp alters the maximum photon energy and the distribution of Bremsstrahlung photons, which directly influences both image quality and radiation dose.