Basic Radiation Physics
Filters

Filters absorb the low-energy photons from the x-ray spectrum. These low-energy photons will not contribute to the formation of an image. In dental x-ray units, the glass of the tube acts like a filter (inherent filtration), and, in addition, we add a piece of aluminum in front of the x-ray tube for additional filtration. We measure the total filtration as an equivalent to a millimeter of aluminum. If the kVp of the tube increases, the total filtration should increase.^3,6,11