Long range x-ray imaging utilizing coded aperture techniques and dynamic reconstruction

Improvised explosive devices (IED) pose a very serious threat to civilians and military forces around the world, and new technologies must be developed for the early detection of these objects. Because of the high concentrations of low atomic number material such as nitrogen and hydrogen present in these explosives, x-ray backscattering provides a viable method of collecting information about these targets by analyzing their shape. Furthermore, a coded aperture used in conjunction with dynamic reconstruction algorithms offers high sensitivity and resolution even while the target is moving towards the detector. This paper describes a lab-based system that simulated a source-target-detector arrangement to be utilized in a radiation detecting vehicle in order to test dynamic reconstruction methods. Using a 225 kVp x-ray tube as the source, a medical CT-system camera fitted with a drill mask of 50% fill factor as the detector, and both radioisotope sources and low Z backscatter targets, images were acquired and reconstructed. The geometry of the experimental setup was optimized to reduce background noise from air scatter and environmental sources, as well as to prevent incident photons from directly reaching the detector from the x-ray tube. Measurements of a Co-60 point source and Co-57 area source with high activity generated high contrast images for which the shapes of the sources were clearly resolved. Acquisitions with varying target-detector distance of low Z materials, including a filled water jug and a four inch thick polyethylene arrow, produced lower contrast images in which the shapes were not as easily distinguished. The radioisotope tests were a proof of principle for dynamic reconstruction and the backscatter targets provided much insight on methods for improving the lab system, including the addition of steel behind the target, the narrowing of the detector energy window, and reassessment of the x-ray cone-beam.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Nuclear Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Lee, Tiffany (Tiffany Ting)

Advisor dc:contributor.advisor

• Richard C. Lanza.

• Nuclear Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/44837

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/44837