Development of X-ray Coherent Scatter Projection Imaging Systems

Coherent scatter x-ray imaging systems are sensitive to material structure and chemical composition, and generate images with contrast superior to conventional transmission x-ray imaging. The goal of this thesis was to develop a scatter projection imaging system capable of acquiring images in less than ten minutes, in the range of nuclear medicine scans, to be practical for future applications such as bone specimen imaging. Two systems were developed. The first improved on the group's previous work and was configured at the Canadian Light Source synchrotron. It employed five 33.2 keV pencil beams in combination with continuous object motion. The system consisted of a primary collimator, motorized stages for object translation, a flat-panel x-ray detector for measuring scattered x rays, and discrete photodiodes for simultaneously measuring transmitted x rays. The acquisition time for a 5.0 cm × 9.0 cm object with 8425 pixels was 2.3 min. Use of continuous motion acquisition increases the width of image boundaries by the product of the object translation speed and the acquisition time per pixel. Contrast-detail performance was independent of acquisition speed. Pixel signal-to-noise ratio (SNR) measurements indicated that the scatter data were limited by the detector readout noise. The synchrotron system was a development stage in an idealized environment but a practical system requires a commonly available x-ray source. Therefore, a second system was developed using a conventional rotating-anode x-ray tube. An array of up to three rows by five columns of pencil beams can irradiate the object simultaneously. A 110 kVp spectrum with 2.25 mm of added Al filtration was used. Motorized stages translate the object through the beams for step-and-shoot acquisition. For this first x-ray tube-based system, the primary imaging capability was not optimized and transmitted x rays are measured through attenuators using the same flat-panel detector that measures scattered x rays. The shortest acquisition time for a 6.0 cm × 10.0 cm object with 6000 pixels was 8.8 min. Contrast-detail performance was similar to the synchrotron-based system. SNR measurements indicated that the scatter data were not readout noise limited.