Radiation exposure can be frightening to some people. However, several points should be kept in mind when considering the risk associated with any radiation exposure.
First of all, we are all continuously exposed to radiation of many kinds, including "ionizing radiation," the type of radiation found in X-ray studies and nuclear medicine exams. Other types of radiation include "infrared" (felt as heat), "ultraviolet" (gives us a tan and hastens the aging process of the skin), and even visible light (allows us to see our environment).
The ionizing radiation we are exposed to comes from the sun, from natural elements in the earth, from the materials used to build our homes, and even from natural radioactive elements in our bodies. Depending upon the region of the world in which we live, we are exposed each year to varying amounts of radiation. In the Boston area, the annual radiation dose is approximately 300 millirads. If you lived in Denver, Colorado, the annual dose would be approximately 600 millirads (mr). Some places in the world have annual doses of over 1,000 mr. Interestingly enough, the places in the world with the higher radiation doses also have
lower cancer rates than those with lower annual doses. This suggests that the cancer rate is not noticably affected by low-dose radiation exposure, and the difference in cancer rate noted is probably related to other variables in the environment, such as exposure to cigarette smoke, automobile exhaust, and carcinogenic chemicals in the environment.
A second point to keep in mind when considering the radiation dose from your medical imaging test is that some radiologic procedures, such as magnetic resonance imaging (MRI) and ultrasound, do not even use ionizing radiation. Magnetic field and ultrasound energy, in the doses used by those tests, have not been shown to cause significant tissue damage.
In tests that do use ionizing radiation, the dose is usually very small, and is often similar to what you would get from natural background radiation in everyday life. As an example, a dose for a typical X-ray procedure might be 30 - 1,000 mr. Other radiologic tests use higher radiation doses, as much as 5,000 millirads or more. Despite extensive study of the effects of radiation, direct evidence does not show that these doses are harmful to humans. Some experts believe that doses of radiation this small pose absolutely no risk.
The radioactive materials used in Nuclear Medicine have very short half-lives, which means that they decay rapidly into a harmless material. Often, the injected radioactive material is only inside the body for a very short time, and the total dose of radiation is small -similar, and sometimes even less than, many other kinds of X-ray procedures. About twelve million nuclear medicine exams are performed every year in the United States.
Examples of Radiation Exposure
(numbers are approximate)
Source of Exposure
Amount in Millirads
|Natural background exposures (from earth, cosmic rays, etc.)
||300 mr per year
||600 mr per year
||1,500 mr per year
|Flying across the country
||6 mr each way
|Living next to a typical nuclear power plant
||1-2 mr per year
|Watching color TV
||2-3 mr per year
Any potential risk of radiation exposure should be balanced against the benefits derived from the exposure. Just as we might accept the risk of riding a bicycle to obtain the benefits of exercise, we should consider that the small risk that may be associated with radiation exposure can be well worth the benefits obtained. For example, a mammogram can detect breast cancer long before it can be felt during a physical exam. This early detection of the tumor can save lives.
Some patients ask, "If the radiation risk is so small, why does the technologist step behind a shield to prevent exposure to themself?" The radiation dose for each exam is relatively small, but over time, the dose can add up. There are many state and federal regulations limiting the total radiation dose that may be received by people working with radiation. To comply with those regulations, the technologist must follow strict precautions to keep their cumulative exposure to a minimum.
Although no adverse health effects have been directly linked to low-dose radiation exposure, the medical community is playing it safe with regards to radiation. Most physicians are very careful about ordering radiologic tests. They should not order a study unless it will improve patient care. If you have a question about the importance or the necessity of a radiologic test that has been ordered for you, be sure to ask your physician.