Energy and dose considerations for diffraction enhanced CT in small animal studies

摘要

Diffraction enhanced imaging (DEI) uses monochromatic x-rays coupled to an analyzer crystal to extract information about the refraction of x-rays within the object. Studies of excised biological tissues show that DEI has significant contrast-to-noise ratio (CNR) advantages for soft tissue when compared to standard radiography. DEI differs from conventional CT in that its refraction contrast depends on x-ray energy as 1/E, thus the energy and dose considerations for conventional CT will be inappropriate. The goal of this study was to assess the optimal energy for in vivo CT imaging of a mouse head to obtain the largest soft tissue refraction CNR. Through a theoretical model, optimum refraction CNR for mouse brain imaging was found to be about 20 keV. The findings were tested experimentally using the DEI system at the X15A beamline of the National Synchrotron Light Source. Using the parameters for optimized refraction CNR (20 keV, silicon [333] reflection), large image artifacts were caused by DEI's scatter-rejection properties. By increasing the x-ray energy and using a lower order diffraction, silicon [111], soft tissue features within the brain, including the hippocampus, could be resolved.