Answer to Question #14662 Submitted to "Ask the Experts"

There is ample evidence to show that medical x rays are safe under normal conditions, but what is the risk of technical or operative malfunctions?

There are three main ways we make sure x-ray equipment is working correctly: regulations, built-in machine safeguards, and medical physicist oversight. There are also physical limitations to how many x rays can be made during an x-ray exam.
Regulations

In the United States, there are regulations that define safety requirements for all x-ray equipment. These regulations limit the amount of radiation a machine can make. For example, the machine produces noise when x rays are being made. A special light also comes on. This prevents x rays from being made without someone knowing.

Built-in safeguards
All x-ray equipment has various safeguards. This helps make sure that it is very hard for the machine to malfunction. For example, every x-ray machine has a "back-up timer" that limits how long the machine can automatically produce x rays. To make the x rays stay on longer, the radiologic technologist must purposely change the machine settings.

Medical Physicists
Medical physicists are specially trained in the safety and quality of medical imaging. One of the things we do is check to make sure that x-ray equipment works according to regulations. We also test the machines to make sure they are working correctly. For example, we test the accuracy of the timer used to control the x rays. Medical physicists are often involved in developing state and federal regulations.

Physical Limitations
Finally, x-ray machines cannot keep making x rays for very long. There are physical limits. These machines make x rays by passing a current, typically between 0.1 ampere (A) and 1 A, across a high voltage (between 80,000 and 150,000 volts). Making x rays creates a lot of heat. If the machine makes x rays for too long, it will overheat and break. The amount of heat created depends on the current and voltage being used for that specific x-ray exam. But here is one example. For typical settings used to take an x ray of an adult's abdomen, the exposure time is about 0.1 seconds. The x-ray tube could stay on for only about 0.7 seconds before overheating. So even if everything else goes wrong, the number of x rays would increase by about seven times. However, this is an extremely unlikely event (and one I have never seen).

There are a lot of things that go into making sure x-ray machines are working correctly. It is a combination of regulations, built-in safeguards on the machines, and people who are specially trained to make sure the machines are working safely.  

Rebecca Milman, PhD
Medical Physicist