Tighter airport security requirements can make traveling a bit more frustrating. Especially with the implementation of the Transportation Security Administration’s (TSA) new full-body image scanners. But imagine being stopped when you set off the alarms—and having no clue as to why it’s happening.

You should know that some diagnostic tests—such as heart, bone or thyroid scans—use radioactive material that can leave traces of radioactivity in your body for up to two months. And this radioactive matter can trigger the airport sensors. Be sure to ask your doctor for written documentation after you’ve had any test that uses radioactive material. It can help you avoid trip delays and embarrassing strip searches.