Answer to Question #10610 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
In the last six months I've had four MRIs (magnetic resonance imaging), one octreotide scan, one biliary scan, two CAT (computerized tomography) scans, and two ultrasounds. Now I'm scheduled for a mammogram in addition to dental x rays and two airport screening x rays. Is this safe? I feel as if I might start to glow in the dark!
The short answer is yes, it's safe, and I'm sure you know people don't actually "glow in the dark" following exposure to ionizing radiation. MRI uses radiofrequency (RF) energy and magnetic fields which, unlike x rays, are nonionizing radiation. Likewise, ultrasound uses sound waves, not ionizing radiation, to produce the diagnostic image. No adverse effects would be expected from either of these exams.
The airport screening you referred to may, or may not, have used ionizing radiation, as many of the airport security passenger screening systems use millimeters (mm) wavelength RF energy, not x rays. It is not obvious to most people which system is being used. However, even if your exposures were from the so-called "x-ray backscatter" security screening systems, the radiation dose is vanishingly small. To put it into perspective, even if there were no x-ray security systems, by deciding to fly, your daily (and largely unavoidable) natural background radiation exposure (approximately 8 µSv) was slightly increased. This is because exposure to natural galactic and solar cosmic radiation increases with altitude due to decreased atmospheric shielding (see the Health Physics Society fact sheet on background radiation for a discussion of sources of background radiation and their average dose). For example, a typical three-hour flight will result in an additional dose of approximately 10 µSv. By comparison, the dose from a typical x-ray backscatter security screening system is approximately 1,000 times less, 10 nSv. Looked at another way, the dose from the x-ray security scan is approximately equal to the additional dose of naturally occurring cosmic radiation that you would receive if your flight time was about 10–15 seconds longer than normal.
The other exams you mentioned do result in small (e.g., dental) to moderate (e.g., CT) ionizing radiation exposure. Nevertheless, the risk from these procedures, when properly performed and clinically indicated, is very small compared to the diagnostic benefit they provide. For more information on doses from medical imaging procedures see the Health Physics Society article Doses from Medical Radiation Sources.
Jerrold T. Bushberg, PhD, DABMP, FAAPM
Editor's Note: The doses from the nuclear medicine scans you received are not listed in the referenced article. They are:
- Octreotide scan (111In Pentetreotide aka Octreoscan): ~ 12 mSv
- Biliary scan (99mTc Disofenin, aka HIDA): ~3 mSv