HARDENING FILTER

Typical Number in Hospital:

Cost Bands:

References: 7

For a particular kV setting on an X-ray set the rays have a range of wavelengths, of which the shorter are less absorbed in tissue than the longer. The intensity of the longer wavelength rays can be reduced by the inclusion of a hardening filter in the X-ray beam. This is simply a sheet of aluminium or copper which attenuates the longer waves (soft rays) more than the shorter waves (hard rays), so that the beam reaching the patient has a higher proportion of hard rays.

It is the harder rays which pass through the patient and form the image, whereas the softer rays are absorbed in the patient, and can therefore be removed with advantage. The filters are sometimes shaped to absorb more of the energy near the centre of the beam in order to even out the intensity at the patient.