F-factor (conversion factor)
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.
Radiation-related quantities
The following table shows radiation quantities in SI and non-SI units.
| Quantity | Name | Symbol | Unit | Year | System |
|---|---|---|---|---|---|
| Activity (A) | becquerel | Bq | s−1 | 1974 | SI |
| curie | Ci | 3.7×1010 s−1 | 1953 | non-SI | |
| Fluence (Φ) | (reciprocal area) | cm−2 or m−2 | 1962 | SI (m−2) | |
| Exposure (X) | C·kg-1 | 1971 | SI | ||
| röntgen | R | esu/0.001293 g of air | 1928 | non-SI | |
| Absorbed dose (D) | gray | Gy | J·kg−1 | 1974 | SI |
| rad | rad | 100 erg·g−1 | 1953 | non-SI | |
| erg·g−1 | 1950 | non-SI | |||
| Dose equivalent (H) | sievert | Sv | J·kg−1 | 1977 | SI |
| röntgen equivalent man | rem | 100 erg·g−1 | 1971 | non-SI |
See also
References
Bushberg et al., 2002. The Essential Physics of Medical Imaging. Philadelphia: Lippincott Williams & Wilkins. (p. 55)