Radiation exposure in medical imaging

General

Effective dose is a quantity that measures the biological effects of radiation on people, particularly the increase in risk of cancer. Effective dose is a useful quantity only when relatively low dose rates are in effect.

When measuring dose the instrument measures the energy absorbed in a given material, which is denoted as absorbed dose (a quantity which has the unit Gy = J/kg). Through calibration, which is done through multiplication by a factor defined by the material’s radiation response, i.e. the effect of radiation on the biological tissue of relevance, the measured absorbed dose is translated to effective dose, which is expressed in a unit called Sievert, abbreviated Sv.

In addition to the amount of radiation (absorbed dose) and the ability of the biological tissue to absorb the radiation, effective dose also depends on the type of radiation to which the biological tissue is exposed. Examples of different types of radiation are electromagnetic radiation (gamma and X-ray radiation), particle radiation (e.g. electron radiation, alpha radiation), and neutron radiation.

Health effects

The sensitivity to radiation differs between organs. Typically, organs with more frequent cell division are more sensitive to sensitive to radiation than other organs.