Color X-ray Imaging Vs Grey Scale
Materials Discrimination imaging is the standard method of viewing an x-ray image with checkpoint security systems. Unfortunately, portable x-ray systems for counter IED operations and the end-users have not embraced this technology, and they are many reasons. The main reason is that they do not understand it and its benefits over a greyscale image. Agencies like TSA, ECAC, and Others have done extensive testing on an x-ray operator's ability to detect an IED threat with greyscale and materials discrimination imaging. The operators could find the threats at a much higher % with materials imaging vs. greyscale in every test they did. The other problem is that most portable x-ray vendors use technology that cannot do accurate materials imaging and nor do they understand it. Adding insult to injury was the ANSI 42.55, creating the "Organic Detection" myth. That single standard and its flawed "organic detection" set the Counter IED community back years.
The Bomb Disposal Community is very disconnected from the checkpoint security x-ray world, which is part of why they have an abysmal understanding of how materials discrimination imaging works. For example, they do not have any idea how much more effective color is vs. greyscale and the studies that prove it. The other huge reason is that the technology they are using is designed for the medical x-ray industry, where greyscale is all they need. The medical x-ray world is looking for density anomalies in an x-ray image, and that is what greyscale provides. Both of the above and the vendors (plus ANSI 42.55 writers) abysmal understanding of how to "accurately" capture dual-energy materials discrimination image have currently doomed the Bomb Disposal community to 20 years behind the rest of the security x-ray world.
To be able to do accurate materials discrimination imaging, you need a measurement of x-ray energy in both a High and Low range. This is where the term "dual-energy" comes from, and it is specifically referring to a system's ability to provide materials discrimination imaging. The "problem" is that you need very stable x-ray energy coming from the beam. To do this, you need an x-ray generator with a very stable energy output across the ENTIRE surface of the detectors. This means that whatever level of the x-ray energy is hitting the center of the panel has to be the same as hitting the corner of the panel. With pulsed x-ray generators and an x-ray beam in the shape of a cone, you are NOT getting this. So when you test an amorphous silica panel DR panel using a Pulsed x-ray source, you get very inaccurate materials discrimination images. For example, you see below a widespread type of dual-energy materials discrimination image from a system using a pulse generator. You can actually see the cone energy change as you move outward from its center, and that change in energy creates massive changes in your material's imaging accuracy.
Pulsed generators also have inferior energy output when you look at it from a scale of how much of the energy is "Good" energy. When you see a kV rating of any x-ray, it tells that is the highest level of kV being out by that system. They do not tell you how much of the energy is at the kV level it is rated. With pulsed systems on, a small % of the kV is actually at the range they list the unit. Constant potential x-ray generators provide a much higher % of the high-end kV that they are listed.
This creates the next problem for a pulsed system in that as the cone gets wider, the photons start getting farther and farther apart, so you end u with less energy interacting with your detectors. It also means that the % of the high kV energy is becoming less and less. This is what causes what you see in the above image, and if you were actually to TEST the portable system using a pulsed generator, you would see this same effect. This makes the dual-energy measurements VERY inaccurate. However, buying these units knows this is happening, and documents like the NIJ and ANSI 42.55 standards do not cover this issue.
With a cabinet x-ray system, they have a "LINE" of detectors vs. an entire large plate like the amorphous silica panels. They also use a collimator to focus the x-ray beam directly on the detectors. A collimator is a widespread tool in the x-ray world and is used to focus the x-ray beam. Collimation of the x-ray beam is a totally foreign concept to the Bomb Disposal community. None of the Bomb Disposal portable x-ray systems makes any effort to focus the energy on the panel. In the medical x-ray industry, they all use collimators to focus the x-ray beam into a square. This really cleans up the scatter and provides a much more stable energy level across the entire surface of the detector panel.
If you have ever had a medical x-ray and you watched the light with the crosshairs coming from the x-ray, that is the collimator. They will adjust it, and the light will get bigger or smaller, and where you see the light is when the x-ray beam is focused. It uses lead (or tungsten) shutters that focus the round beam into a square (HOLY CRAP!!!). These shutters are adjustable, and the light with the crosshairs lets you see exactly where you have focused them x-ray beam. So instead of shooting a circular x-ray beam at a square detector panel, the medical world collimates the x-ray beam into a square. The only people who do not use a collimated x-ray beam and are still shooting a circular beam at a square target are Bomb Disposal Technicians.
The circular x-ray beam coupled with a very inaccurate and unstable x-ray generator creates a nightmare scenario for trying to accomplish accurate materials discrimination imaging. The people trying to engineer these portable systems and the people who are writing the standards are utterly clueless on how to do dual-energy imaging accurately. This is why you end up with made-up and very flawed concepts like "Organic Detection". I have written about this before and organic detection is one of the worst things that ever happened to the bomb disposal x-ray market. It is literally the main reason they are stuck with technology that is a mix-and-match train wreck.
So how does a cabinet x-ray give you accurate materials discrimination imaging?
The first thing they do is use a constant potential x-ray generator that provides a kv output that is very stable kV output when you compare it to something like a pulsed generator. Stable x-ray energy is vital, and if it is jumping up and down, your material's measurements will be inaccurate. The next very important thing they do is collimate the x-ray beam, so it is only hitting the detectors and not just spraying the x-ray all over the place.
When a technician sets up a cabinet x-ray, they look at the energy at each detector in the software diagnostic tools and make sure it is the same for each one. They also verify the high and low energy measurement at the detectors to ensure it is the same at each detector. They do this with a software feature called a "line scope".
They also use detectors that are set up with high and low energy detectors. One has no filter, and the other uses a copper filter. So the x-ray generator fires at a set kV (typically 140-160 kV) all of the time, and the detectors have the ability to collect a high and low energy measurement in a single scan. These are constant potential x-ray generators and they use them because they provide very stable x-ray energy output, unlike a pulse generator.
The main point is that when you look at the Bomb Disposal community x-ray technology it is a mix and match of components from other x-ray industries. It was never "designed" for the counter IED operation mission and it honestly a poster child for the term "Ad Hoc". When you take the time to really learn how the medical and security x-ray industries have engineered their technology for mission-specific applications you see just how far behind-the-counter IED x-ray systems are. The only way this is going to get fixed is for the counter IED subject matter experts to get much smarter about x-ray and more important step outside the bubble of what they currently know. Until that happens and intelligent standards and engineering are applied to the technology it will continue to be an Ad Hoc mix and match of technology.