Answer to Question #4797 Submitted to "Ask the Experts"

Interesting question and one for which I'm not able to get very specific because I've been unable to find any information about the x-ray units used for this screening. Based on my experience, though, let me run a couple of things by you.

In general, the effective dose from a standard abdominal x ray used for medical reasons is around 40 millirem (mrem). The x rays taken for most medical exams will normally be a bit more energetic because we want less contrast (more black and white, fewer grays) in the picture. When we have less contrast, we can see things like air in the bowel and small fractures in bone.

So, that gives us a baseline—the 40 mrem—which may be on the high side for an x ray that is taken to detect contraband inside a person. I would think that, to detect contraband inside someone, more contrast would be better. That, in turn, means the technique factors used to make the x ray would be lower so it would be a lower dose to the person.

Another way to gain more contrast is to remove a grid that is normally between the person and the x-ray film. The grid is there to remove low-energy x rays. When the grid is gone, the technique factors can be reduced.

Bottom line: We can use the 40 mrem as an estimate of the dose received for this type of abdominal x ray. The dose might be higher but it is more likely that it is lower. As a comparison, we each receive about 360 mrem each year from naturally occurring radiation sources. It's a fairly low dose but higher than what our luggage receives when it goes through a security scanner.

Just another note—there also are personnel contraband screening machines used that do not use ionizing radiation. They use millimeter-waves (like radar). Everything in your body emits heat other than the contraband and this unit takes advantage of that by looking for non-heat-generating items. Maybe this is what was used in your example.


Kelly Classic
Certified Medical Health Physicist