Monte-Carlo simulations of a coded-aperture x-ray scatter imaging system for molecular imaging

In this work, we demonstrate the ability to determine the material composition of a sample by measuring coherent scatter diffraction patterns generated using a coded-aperture x-ray scatter imaging (CAXSI) system. Most materials are known to exhibit unique diffraction patterns through coherent scattering of low-energy x-rays. However, clinical x-ray imagers typically discard scatter radiation as noise that degrades image quality. Through the addition of a coded aperture, the system can be sensitized to coherent scattered photons that carry information about the identity and location of the scattering material. In this work, we demonstrate this process using a Monte-Carlo simulation of a CAXSI system. A simulation of a CAXSI system was developed in GEANT4 with modified physics libraries to model coherent scatter diffraction patterns in materials. Simulated images were generated from 10 materials including plastics, hydrocarbons, and biological tissue. The materials were irradiated using collimated pencil- and fan-beams with energies of 160 kVp. The diffraction patterns were imaged using a simulated 2D detector and mathematically deconstructed using an analytical projection model that accounted for the known x-ray source spectrum. The deconstructed diffraction patterns were then matched with a library of known coherent scatter form-factors of different materials to determine the identity of the scatterer at different locations in the object. The results showed good agreement between the measured and known scatter patterns from the materials, demonstrating the ability to image and identify materials at different 3D locations within an object using a projection-based CAXSI system.