Monochromatic X-Ray CT Using Synchrotron Radiation

This paper describes a prototype monochromatic X-ray CT using synchrotron radiation and evaluates its spatial resolutions, noise in reconstructed images, and quantitatively. A monochromatized X-ray using a crystal spectrometer is passed through a slit (width 25 mm, variable height 25 μm to 2.5 mm), and then irradiated on a rotating sample. The X-ray passed through the sample is converted into an electrical signal by using an X-ray detector with 1024 channels, and then fed into a computer input. This monochromatic X-ray CT has a view field 25 mm in diameter. The CT has an X-ray spectroscopy function and a direct magnifying function of projection using an asymmetrical Bragg reflection, as well as a function for conventional cross-sectional images. This paper describes theoretical analyses of the spatial resolution and noise in reconstructed images which determine the capability of an X-ray CT, and the experimental evaluation of the prototype CT. Theoretically, the spatial resolution is expected to be greater than 25 μm at a magnification of 5, and this agreed with experimental results, as well as the theoretically determined noise in reconstructed images. The prototype apparatus has an energy resolution of 0.1 percent (full width of half maximum) in an energy range of 7 to 40 keV. This makes an absolute-value measurement of the X-ray absorption coefficient possible, and this has been confirmed experimentally. By using this apparatus, it is possible to produce an image quantitatively indicating the distribution of a particular chemical element.