Imaging characterization of a multi-energy CT with quasi-monochromatic X-ray source

Abstract

A new multi-energy computer tomographic system for small animals (MECT) was developed - and is now operative - with a quasi-monochromatic X-ray source. The system brings together two important features: the possibility to scan small animal with quasi-monochromatic X-ray beams and the possibility to select a multiple energy algorithm for the imaging reconstruction. The medical imaging with monochromatic beams is in fact the new frontier since it allows a new way to visualize selectively different tissues by injecting contrast medium but also without using it. Indeed, an Alvarez-Macovsky like algorithm can enhance the sensitivity of the imaging system to a contrast medium provided with a K-shell binding energy (for example, the iodine has a K-edge at 33.2 keV and the measured sensitivity enhancement is of about 10 times). Moreover, using monochromatic X-ray beams with different energies, it is possible to measure, point-by-point, the tissue density, the electron density and the effective atomic number, exalting the physicochemical information of tissues. These data are all available with a patient scanning using two (or better three) quasi-monochromatic X-ray beams at different energies. However, with a new reconstruction algorithm based on three different energy beams, the so-called projection artifact (due to not homogeneous density of the background) can be corrected, making the tissues separation and the visualization of very low concentration of contrast medium available. This facility and the new reconstruction algorithm, was developed to study, on small animals, the possibility to introduce new methods for the earlier diagnosis of the tumors, by exalting the precancerous tissue changes as, for example, the neoangiogenesis. Aim of this work is to discuss the imaging proprieties of the quasi-monochromatic CT, using both the images of dedicated phantom and in-vivo images of small animals.