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.
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