[ RadSafe ] Z-Backscatter technology

[Bradt, Clayton (HEALTH)]

Thanks, Brad. You confirm some of my conjectures about how this works, but I never considered that the side of the van itself was the detector. Others have recently suggested that the dark regions that appear to be lung cavities are actually artifacts of the imaging software. This may well be the case. However, I reason that  x-rays from the interrogating beam able to penetrate the sides of the scanned vehicle AND produce Compton backscatter able to penetrate the same vehicle on the way back to the detector would have to be of reasonably high energy so that the return signal is not swallowed up by attenuation.  This means that the device must employ x-ray energies that are sufficiently penetrating to produce density information from the chest cavity and result in those dark regions in the image.  Now I hate having to rely upon conjecture and wish someone would be able to give me an authoritative explanation of how this technology works.  After all, someone must have evaluated and approved the use of these devices -right? I hope that whoever did so reads RADSAFE and will respond in due time.  Now, here's the kicker:  In most states, including New York, the intentional application of ionizing radiation to humans requires a physician's order, and the presence of a licensed, registered radiological technician.  There are no law enforcement or "national security" exceptions in the code.  How on earth can NYPD be legally scanning occupied vehicles?



Clayton Bradt

Principal Radiophysicist

NYS Dept. of Health





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From: Brad Keck <bradkeck at mac.com<mailto:bradkeck at mac.com>>



Clayton,



If i understand the Z-backscatter physics correctly, then the dark images of the lungs result from a lesser backscatter signal being generated in the lung cavity versus the thicker surrounding tissues.



Unlike an airport scanner, which does not need to penetrate the side of a truck, the cargo scan uses a higher energy (and intensity, i would think)  x-ray source which penetrates humans more than the energies used in airport scans.  The detector array - basically the side panel of the truck - is then used to measure the intensity of the x-rays corresponding to those scattered by low-Z material so you build an image of the low-Z materials in the first few centimeters lying along the side of the truck, including humans, drugs, explosives, cantaloupes, etc?.   Interestingly, both air and high-Z materials would give a ?dark? image, where any organic or low-Z materials would give a ?bright? image under the acquisition parameters used.



There are numerous dose estimates on the internet for the airport scanners, but I have not seen estimates for the cargo scans where a human might inadvertently be present.



Hope this helps,



Brad




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