X-ray are electro-magnetic waves that form part of the electro-magnetic spectrum. This spectrum also includes micro-waves, infra-red and visible light.
The electro-magnetic spectrum is made up of electromagnetic waves, vibrations of electric and magnetic fields that propagate through space. These waves travel at the speed of light: 300 million meters per second, or 669.6 million miles per hour!
Every electromagnetic wave exhibits a unique frequency and a wavelength associated with that frequency. For instance, this picture represents an electromagnetic wave corresponding to the colour red.
Its frequency is 428 570 GHz (pronounced gigahertz), which can also be stated as 428,570 billion cycles per second. So when you look at red light, your eye receives over four hundred trillion waves every second!
The wavelength of such light is just 700 nanometres long ,which means that one wave spans only 7/10 000 000, or 7 ten millionths of a meter.
All electromagnetic waves are classified according to their characteristic frequencies, and this is the electro-magnetic spectrum.
Just as red light has its own distinct frequency and wavelength, so do all the other colours. Orange, yellow, green, and blue each exhibit unique frequencies and consequently wavelengths. While we can perceive these electromagnetic waves in their corresponding colours, we cannot see the rest of the electromagnetic spectrum.
Visible light falls within a very narrow range with in this spectrum. Most of the electromagnetic spectrum is invisible, and exhibits frequencies that traverse its entire breadth. Exhibiting the highest frequencies are gamma rays, x-rays and ultraviolet light. Infrared radiation, microwaves, and radio waves occupy the lower frequencies of the spectrum.
Whilst the visible portion of the spectrum is harmless, the higher frequency waves can ionise atoms and in this way disrupt body cells on a molecular level. It is therefore important to limit unnecessary exposure to such waves, although we can never avoid them entirely since they are naturally occurring.
X-ray equipment is used to produce images by passing a beam of ionising radiation through the body and recording it onto a photosensitive film or screen. The degree to which the beam is absorbed or scattered during its passage through the body determines the amount reaching the film and hence an image can be produced.
Over recent years, technical developments have seen the introduction of 'filmless' imaging, where the image is displayed on a computer monitor and stored in an image database.
This, and other advances, have resulted in a reduction in the radiation dose for many medical imaging examinations.