Filtration and X-ray intensity

• Imaging systems use metal filters, usually 1 to 5 mm of aluminum (Al), positioned in the useful beam.
• The purpose of x-ray beam filtration is to reduce the number of low-energy x-rays incident on the patient.
• Low-energy x-rays contribute nothing useful to the image and only increase the patient ESE unnecessarily because they are absorbed in superficial tissues and do not penetrate through the patient to reach the image receptor.
• Adding filtration to the useful x-ray beam reduces patient radiation dose.
• Filtration in the x-ray beam reduces patient radiation dose because fewer low-energy x-rays are in the useful beam.
• The reduction in exposure due to filtration is not proportional to the thickness of the added filter but is related in a complex way.
• The disadvantage of x-ray beam filtration can be reduced image contrast caused by x-ray beam hardening.
• X-ray beam hardening increases the number of high energy x-rays in the beam by removing the lower-energy nonpenetrating x-rays.