Development of a Multi-Energy CT for Small Animals: Characterization of the Quasi-Monochromatic X-Ray Source

A new multi-energy CT for small animals is operative (now only in scanning mode) at the Physics Department of the University of Bologna. The system makes use of a set of quasi-monochromatic X-ray beams produced by means of an Highly-Oriented Pyrolytic Graphite Bragg monochromator. This source is able to provide beams with energy tunable in a range from 20 to 70 keV. Here we present a complete characterization of the source. A theoretical model of the source has been analyzed, according to the known Zachariasen's theory for diffracting crystals. The beams have also been characterized in resolution and intensity, over the accessible range, and we present here some measured spectra. The monochromator system demonstrated an energy spread of about 3 keV (Full Width at Half Maximum-FWHM) at a beam energy of 26 keV. At the same energy, the intensity of the output beam is about 6% of the primary beam.