Radiologists wish to keep the amount of radiation during a medical imaging exam “As Low As Reasonably Achievable” – known as the ALARA principle – but just how much radiation are we receiving?
First we need to be able to quantify it. Radiation dose is measured in units of Gray (Gy) which is proportional to the amount of absorbed energy per unit mass. In turn, the absorbed energy is proportional to the physical damage on the cell’s chemical bonds- such as DNA double strand breaks.
Radiologists determine how changes in techniques impact radiation dose and image quality, which helps your physician determine whether the benefits from the diagnostic information outweigh the exposure risks of the exam. It should be noted that in most exams the benefits far outweigh any measurable risks.
Reporting and monitoring of dose also enables hospitals to track dose and ensure that patients are receiving acceptable levels of radiation based on established guidelines.
Effective dose is an another measure of dose which quantifies the risk associated with an exposure and is reported in Sieverts (Sv). The Sievert allows comparison of the risk estimates associated with partial or whole-body radiation exposures. This quantity first requires the measurement of organ dose (in Grays) and incorporates the different radiation sensitivities of the various organs in the body. This evaluation tool is useful for comparing exposure levels across different x-ray imaging system and from different sources – man made or natural. The chart below compares imaging procedures with natural background radiation, that is, how long it would take to receive the same amount of radiation (effective dose) from the natural background in a normal environment.