F-factor (conversion factor)

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Relation between some ionising radiation units Radiation units.svg
Relation between some ionising radiation units

In diagnostic radiology, the F-factor is the conversion factor between exposure to ionizing radiation and the absorbed dose from that radiation. In other words, it converts between the amount of ionization in air (roentgens or, in SI units, coulombs per kilogram of absorber material) and the absorbed dose in air (rads or grays). The two determinants of the F-factor are the effective atomic number (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.

Contents

The following table shows radiation quantities in SI and non-SI units.

Ionizing radiation related quantities
QuantityUnitSymbolDerivationYear SI equivalent
Activity (A) becquerel Bqs−11974SI unit
curie Ci3.7×1010 s−119533.7×1010 Bq
rutherford Rd106 s−119461000000 Bq
Exposure (X) coulomb per kilogram C/kgC⋅kg−1 of air1974SI unit
röntgen R esu / 0.001293 g of air19282.58×10−4 C/kg
Absorbed dose (D) gray Gy J⋅kg−11974SI unit
erg per gramerg/gerg⋅g−119501.0×10−4 Gy
rad rad100 erg⋅g−119530.010 Gy
Equivalent dose (H) sievert SvJ⋅kg−1 × WR 1977SI unit
röntgen equivalent man rem100 erg⋅g−1 × WR 19710.010 Sv
Effective dose (E) sievert SvJ⋅kg−1 × WR × WT 1977SI unit
röntgen equivalent man rem100 erg⋅g−1 × WR × WT 19710.010 Sv

See also

References

Bushberg et al., 2002. The Essential Physics of Medical Imaging. Philadelphia: Lippincott Williams & Wilkins. (p. 55)