On the average, people in the US are exposed to about 3 millisievert (mSv) of radiation a year a millisievert is just one type of measurement unit for radiation dose, also called the effective dose which would refer to the average radiation risk of the entire body. However, more and more people are getting medical procedures involving radiation, increasing an individuals radiation exposure. In 2006, about 435 million procedures used radiation for either diagnostic or therapeutic purposes.
When it comes to medical radiation, different areas and organs of the body have different sensitivities to radiation exposure. Furthermore, the risk involved varies depending on the procedure type, the number of procedures, the area to be imaged, and the patient, specifically their medical history, age, and sex.
In general, radiation becomes potentially dangerous to people when it reaches high levels. In light of growing concerns, experts have been able to relate the radiation from medical imaging procedures to ones exposure to natural background radiation. For a better understanding of the diagnostic imaging procedures and your risk of radiation, check out this infographic by Radcal Corporation.

Source: radcal.com