X-ray Spectrum and Filtration

back arrow       forward arrow

When x-rays are produced in an x-ray tube, not all of the x-rays are created at the maximum, or peak, energy. A continuous x-ray spectrum is produced which contains x-rays of energies from zero to the kVp.  For most X-Ray spectra the average energy of the X-rays produced are:

EAverage = 1/3 EMax  



Filtration

Since lower energy x-ray photons are unable to penetrate the patient, they cannot add information to the x-ray image. These x-rays contribute radiation dose to the patient, but do not enhance the diagnosis. Since these low energy x-rays are less penetrating, they can be selectively removed from the x-ray beam by adding filtration. The walls of the x-ray tube itself provide some filtration, and additional filtration is typically added in the form of a few millimeters of aluminum. This reduces unnecessary exposure to the patient. Filtration will alter the x-ray spectrum, as shown below.

Filtration

back arrow       forward arrow