use of filters and screens

Filters are used in radiography to attenuate low-energy x-ray photons that do not contribute to image quality but add to patient dose. There are two types of filtration: inherent from components in the x-ray tube, and added from interchangeable metal sheets usually made of aluminum, copper, or tin. The total filtration is the combination of inherent and added filtration, with a minimum of 2.5 mm aluminum required by guidelines. Filters absorb lower-energy photons to produce cleaner images with less scatter and reduce dose, while hardening the x-ray beam by increasing its average energy. The amount of filtration is specified based on kilovoltage and desired beam quality.