Most of the radiation humans receive is from natural sources. We are constantly exposed to radiation of all types - including ionizing radiation like that used in radiology - from our environment. The spectrum of radiation we are exposed to ranges from radio waves, to infrared (heat), visible light, ultraviolet, X-ray, to gamma.
We are exposed to ionizing radiation from natural elements in the earth, from radon in our homes, from the sun, even from foods that we eat. Our exposure to natural radiation is very much dependent upon where we live. A person living in South Bend, Indiana, receives about 300mr (millirads) of radiation a year. A person in Colorado could expect to receive as much as 800mr per year. Some places on Earth expose persons to many thousands of millirads of ionizing radiation from natural background sources per year.
These amounts are comparable to what you can expect to receive from a radiologic test. Most tests range from 10 to 1000 mr. No studies of radiation exposure in humans show harmful effects at these levels of exposure.
You may notice that the technologist steps behind a shield during your exam. This is because the small exposures for each exam can add up over time; some technologists perform as many as 30 examinations per day. State and Federal regulations prohibit persons working with radiation from having exposures over a certain level. Our staff are monitored to prevent the possibility of reaching this level through cumulative exposures.
We practice the concept of ALARA (As Low As Reasonably Achievable) for radiation exposure to our patients. In contrast, ultrasound examinations use no ionizing radiation at all.
Physicians will not order a radiologic test unless it will benefit patient care. Consult your physician if you are concerned about the necessity of a radiologic exam you are about to have.