Answer to Question #5822 Submitted to "Ask the Experts"

I had a HIDA (hepatobiliary iminodiacetic acid) scan done today and asked the technician whether I needed to stay away from my children for any length of time. She said it was no problem with the technetium, as if I had not received radioactive iodine or something more potent. Immediately after my HIDA scan, I came home and rocked my one-year-old to sleep and ended up taking a nap with him. I was in very close contact with him for almost three hours. This was all within the first couple of hours after the injection. The scan took less than an hour and a half, and I live two minutes away from the hospital, so my first contact with him was less than two hours after the injection.

Only afterward did I find a posting on your Web site that recommended avoiding contact with small children for a few hours after a HIDA scan. What danger could I have exposed him to? What risks are associated with technetium exposure in small children? Can you give me an idea of what sort of radiation dose he may have received? Should I have him evaluated for some sort of disorder in the future?

I can understand your concern about the information that the nuclear medicine technician gave you after your HIDA injection and scan. If you had asked the same question of technicians at my hospital, they would also have told that you there were no restrictions. Nevertheless, if you were concerned about exposing your children, they would recommend that you could maintain some distance from your children for the rest of the day.

The exposure your child received was very low and should not be a concern. The positive side of this situation is that a HIDA scan uses a small dose of technetium-99m, typically about 300 MBq (8 millicuries), which is less than most other nuclear medicine studies using technetium-99m. I assume that you were not administered cholecystokinin. While it is commonly used following the first HIDA scan, it takes another 30 minutes of imaging. One hour of imaging is the smallest time possible for the HIDA scan.

I estimated the radiation dose to your child from measurements of nuclear medicine patients after injections of ^99mTc (technetium-99m). I assumed radioactive decay and no voiding, which would have further reduced the dose. My estimated dose to your child was about 0.14 mSv for the three hours after your imaging scan. This dose is not a concern to health of your child, and many radiation experts would say it is not dangerous. Adverse effects of radiation exposures have not been demonstrated in exposures below 100 mSv, as noted in the Health Physics Society Position Paper "Radiation Risk in Perspective." The position statement says in part, "Below 100 mSv. . . risks of health effects are either too small to be observed or are nonexistent." Also, there is no test that can be done to determine any detrimental effect to your child at this very low radiation dose.

As some points of reference, I can give you some examples of radiation doses that people receive from natural background radiation. Natural background radiation includes cosmic radiation, material in the earth, and naturally occurring material in food and water. If you lived in Denver, your child's dose from natural background radiation is approximately 0.03 mSv in one day. The radiation dose from a coast-to-coast airplane flight is about 0.04-0.05 mSv. So the dose from your time spent close to your child is similar to the dose from three airplane flights or being in Denver on vacation for five days.

Marcia Hartman, MS
University of California Davis Health System

Editor's Note: The information on the natural background exposure in Denver is from the Institute for Science and International Security Web site. The value is listed as 11.8 mSv/year exposure from radon, cosmic, and terrestrial radiation, food, and water.