X-ray imaging has been used to examine the internal structure of objects ever since Wilhelm Roentgen took the first radiograph of his hand in 1895. Since then imaging technology has developed enormously and has developed into the sophisticated tools that find application in hospitals and industry.
Almost all of these are based on the transmission of X-rays through an object to create a shadow picture of its internal structure. This requires access to both side of an object, which can present a problem in some security applications where objects either cannot be moved or are too large to accommodate in a conventional imaging system.
An alternative approach is to use X-ray backscatter imaging which interrogates objects from only one side by illuminating them with an X-ray beam and collecting the X-rays that scatter. Unlike transmission radiography a focusing element is required to form an image. Conventional lenses don’t work for X-rays so a more novel approach is needed such as a pinhole system or coded mask such as is used for far-field X-ray astronomy. In this case the image formed on the detector is encoded with the mask pattern and image processing is required to decode the true image of the object.
In this project the researchers are working with their research sponsors at Dstl to create a prototype X-ray backscatter imaging system through the combination of computer modelling and the construction of an experimental test bed.
The Monte-Carlo code PENELOPE is being used to recreate the entire imaging process from the illumination of the object with an X-ray beam and the physics of the scattering processes inside it to the collection of the scattered X-rays by a coded mask – detector system. An experimental test bed has been constructed based around a compact X-ray generator as found in many baggage scanners and an iCCD detector. Different coded mask designs are being investigated and the results compared to those from the computer modelling. Methods of decoding the true image of the object without introducing artefacts are also being examined, with the aim of producing a high quality image with minimal exposure time.