Compton Scattering in Plain Radiographic Imaging

Compton scattering is a partial absorption reaction involving medium energy x-rays. With the increasing number of peak kilovolts in photon energy, the x-ray releases some of the electron's energy from the outside of the shell in an absorbing medium. The electron is ejected, and the x-ray is deflected away from its intended direction. As a result of the photon energy loss, a longer wavelength x-ray is scattered. The energy loss is proportional to the angle of deflection. Backscatter is the term for radiation that scatters 180 degrees back in the tube's direction.

Scatter radiation causes the image receptor to get inaccurate information, fogs the film and reduces image visibility. Scatter darkens the film's overall tone, though not in a manner that generates helpful information.

The likelihood of an x-ray undergoing Compton interaction is determined by the absorbing medium's density and the energy of the x-rays. The highest amount of scatter radiation is produced by water-density tissues such as muscle, blood, and solid organs. Greater density tissues, such as bone, have a higher x-ray absorption rate. Low-density tissues with air such as the lung and big gut allow x-rays to penetrate deeper. Higher-energy x-rays have a higher penetration rate, whereas medium-energy x-rays have a higher partial absorption rate (scatter), and lower-energy x-rays have a higher overall absorption rate.