Portable X-Ray Basics: Avoiding Lower Edge image cut off

X-RAY Basics Rule Number 1: Never raise your x-ray off the ground

If the item you are x-raying is on the ground and your panel is on the ground behind it, your x-ray generator (aka camera) needs to be at ground level too. The reason is because raising up the generator can cause the lower part of the package to be cut off and not imaged. In the below image you see that with the generator elevated part of the package will be totally missed.

The next image is an x-ray of a package with the x-ray generator evaluated off of the ground. The IED is in the front part of the package (20-35 cm) and is completely missed in the x-ray image. The only thing you can see are the 2 batteries at the very back of the package and a very small part of the battery at 10 cm. You can try and move your generator back but it will only help a very small amount if your generator is elevated. We demonstrate this with the red dotted lines that your visible image is basically a line from the edges of the detector panel detection area back to the x-ray generator (aka camera).

If the package is under 10 cm out from the detector panel you might be "OK" but that is not very realistic thinking. Most things we end up x-raying will come out much farther than 10 cm from the panel. The bottom line is that if your x-ray generator is elevated off the ground you WILL cut off part of the bottom part of the package. When you look at the examples below of several different x-ray deployments you see that all of them have the generator elevated but the panel and package are at ground level. None of the below examples are effective and will cut off a significant part of the lower part of what you are x-raying. This is not a good way to take a x-ray especially for counter IED operations.

In the below image we have lowered the x-ray to the ground level and shot the same test box and you can see a significant difference. We are now able to see more of the items in the box from the 10 cm point and outward. Having the generator on the same level as the detector panel and package is a much more effective method and will provide you a more complete image of the package.

The lower you can get your generator to the ground the better the overall effect. Lower edge cut off is not just the detector panels dead zone. Lower edge cut off is actually a combination of generator height, distance generator is from the front of the package, and panel dead zone. All three of these will factor into how much of the lower part of the package will (or will not) be imaged.

One thing you need to also consider is if the package is as tall as the top of your panel. In this case the top part of the package will be cut off moving out from the panel. The only correction for this is to move the panel and take a second image. This can even affect the sides of the package if the package it very large. You should be able to tell when you look at your image that part of it is being cut off and adjust accordingly. The major issue is lower edge cut off and for counter IED operations this will typically be what is effected the most when you elevate your x-ray generator.

The question now is why are people elevating their generators? One reason is engineers like to shoot at the center of the panel but appear to not fully grasp how it can potentially hide a threat. The other reason is that we are not very good at x-ray basics when it comes to portable x-rays. For any vendor to engineer anything like this means they just do not understand the basics and more importantly grasp the counter IED mission. However, I do not blame the vendors because the experts are supposed to be us Bomb Technicians. We should be telling the vendors what they are doing is wrong and driving them to build better and more efficient systems. Any Bomb Technician should look at any elevated x-ray and automatically see the problem but I am not seeing this. When I teach advanced portable x-ray this one section in the training is typically a lesson none of them knew. I find that very odd and is a major reason why I wrote this article.

Here are a few things you should consider when looking at your portable x-ray system:

1. If your panel is on the ground and the package is on the ground, your generator needs to be on the ground too.
2. Anything that is engineered to elevate the x-ray generator higher than the detector panel WILL CUT off the lower part of the package.
3. Mounting a x-ray generator to a robot chassis elevates the generator higher than the panel and is a very ineffective approach.
4. XTK Gird aim is awesome but.....you are going to get lower edge cut off because of the stand. You cannot target what you cannot see.
5. Your x-ray is 100% about getting an image and seeing if you have a threat. Anything that hinders that ability is not a good idea.
6. Digital radiography detector panels all have a dead zone at the bottom. Most of these were specifically designed for medical applications and dead zones are not a issue. Any detector panel that has over a 3mm dead zone is something you want to avoid. Anything over 3 mm is cutting off a significant part of the package and you should not purchase that for counter IED Operations.

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