In the graph above we show typical dose ranges for different types of exposure to ionizing radiation. Most will not expose the patient to enough radiation to cause a significant increase in risk of harm, but you can see there is a large range of exposures for some of the tests shown in the figure, and ideally patients would get doses at the lower range of dose, rather than the higher range. Also we do not know how these different exposures add up. We are still learning a lot about radiation and exposures, and it is not clear yet how long the effects of radiation are felt. The best advice is to limit your exposure to radiatio where possible. If you need a test, try to get the test in such a way as to minimize your exposures.

By talking with your provider and asking questions about your imaging exam, it is possible to influence the radiation dose you receive. Ask to learn more about the exam. Find out if there are alternative options that do not require you to be exposed to radiation. If the test is necessary, ask your doctor to use the lowest dose of radiation possible.

Sometimes a patient receives repeated exams every few months, or annually. In this case, be sure to talk with your doctor about the necessity of repeating the tests.

What is the average person’s yearly dose of radiation?

The average American has a yearly radiation dose of 6.2 mSv, evenly divided between natural and man-made sources (which includes medical scans, like X-rays or CT scans). If you don't undergo any medical imaging tests, your dose is around 3 mSv per year. More information can be found HERE

What are the largest sources of radiation for the average person?

If you have undergone a CT scan, that is likely the largest single exposure to radiation. If you have undergone a nuclear medicine test of your heart, that could also be your largest source of radiation. Otherwise, for most people the largest source of radiation is from natural sources. Radon — a radioactive gas naturally produced by the breakdown of radioactive elements within the earth. Radon is the biggest naturally occurring source. Cosmic rays are the next largest source of radiation. Some are blocked by the earth’s atmosphere so exposure increases based on altitude.

What are the units of measurement for radiation?

The most common unit is Sieverts (Sv) or milisieverts (mSv).

What is a "mSv"?

A mSv (milliSievert) is how scientists measure radiation, in what we call the "effective dose". Radiation is absorbed differently by different bparts of the body. "mSv" is used to measure the average amount of radiation absorbed over the entire body.

How much is too much?

There are limits in allowable exposure to ionizing radiation if it is received as an occupational exposure (part of someone's job). In Europe, the limit is 20 mSv per year, and in the United States the limit is 50 mSv per year. There are no limits of radiation when used as part of medical care. It is important that any decision regarding whether you should get a test balances the expected benefit of the test, versus the small risk it conveys.

Is it Cumulative?

Radiation is not stored in the body, but the effects of a person being exposed to radiation add up over time. With each exposure to radiation a person has in their lifetime, there is increased risk of harm. A small dose of radiation (like getting one dental x-ray) carries very low risk. The higher the dose of radiation, the greater the risk.