Filters are metallic sheets that are designed to mainly absorb the low-energy x-ray photons from the spectrum. If unfiltered these low-energy x-ray photons are absorbed in the patient, thus not contributing to image formation and just increase dose. Therefore using a filter reduces the patient dose. The process is called filtration and is of two types:

  • inherent filtration, i.e. tube and housing (equivalent to 0.5-1.0 mm Al)
  • added filtration ("hardening"), e.g. aluminium and copper 

Total filtration is the combined effect of inherent and added filtration, with US guidelines stating a minimum total filtration of 2.5 mm of aluminium is required for x-ray tubes operating above 70 kVp 3.  

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Article information

rID: 29737
Section: Physics
Tag: stub
Synonyms or Alternate Spellings:
  • Filter
  • Filtration
  • Hardening

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