Interaction of X-rays with tissues

• A photon of electromagnetic energy ejects an electron from an inner shell of an atom.
• The displaced electron can ionize other atoms.
• An electron from a higher orbiting shell drops into the vacant space releasing energy ’Characteristic radiation.

• Important at low energy.
• Proportional to cube of atomic number ’ small variation in atomic number ie in body tissue ’ large contrast in film exposure.
  Photoelectric absorption is important at kV<100 and at high kV reduced film contrast occurs because photoelectric effect less important.

• A photon of electromagnetic energy interacts with a loosely bound electron in the outer shell of an atom.
• The photon displaces the loosely bound electron which can ionize other atoms.
• The photon is diverted and continues in a different direction with a lower energy ’Scattered radiation.

• Increases with increasing energy.
• As energy increases more of scattered radiation is directed in a forward direction, ie more likely to reach x-ray film.
• Independent of atomic number of tissue.
  Compton scatter is significant at kV>70 and in tissue of low atomic number, ie most body tissue.

Production of scatter

Scatter reduction

Grids

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.