A stream of high energy electrons produced by an electron gun accelerate from a cathode filament and strike a rotating tungsten anode. X-ray photons are generated within the anode which rotates to dissipate heat. The beam of X-ray photons is shielded and coned to reduce the scatter of X-rays produced

High energy electrons collide with and eject an inner shell tungsten electron (green) with subsequent promotion of an outer shell electron (red) to take its place. X-ray photons of a uniform ‘characteristic’ energy are generated

A high energy electron that passes near a tungsten nucleus is deflected and decelerated with generation of an X-ray photon. X-ray photons of variable energy are generated in this way and therefore a non-uniform energy spectrum is produced. This is known as Bremsstrahlung ‘Braking’ radiation

Bremsstrahlung radiation produces a wide spectrum of X-ray energies within the X-ray beam. Characteristic radiation generation however produces a relatively narrow band of X-ray energy. Imaging techniques optimise this characteristic band of X-rays in producing a radiograph

A chest X-ray (CXR) is usually taken with the beam passing from posterior to anterior (PA). The X-ray beam is divergent and so the resultant image is magnified. The closer the patient is to the detector the less magnification is produced. X-rays which hit the detector uninterrupted appear black on the image. Those X-rays that pass into thick structures (e.g. heart) or dense structures (e.g. bones) are attenuated and appear white. Other structures such as the lungs and soft tissues appear as a range of grey, according to their density