The
F-factor, in
diagnostic radiology, is the conversion factor between
exposure and
absorbed dose. In other words, it converts between the amount of ionization in air (
roentgens or
coulombs/kg) and the absorbed dose in tissue (
rads or
grays). The two determinants are of the F-factor are the
effective Z of the material and the type of
ionizing radiation being considered. Since the effective Z of air and soft tissue is approximately the same, the F-factor is approximately 1 for many x-ray imaging applications. However, bone has an F-factor of up to 4, due to its higher effective Z.