Caratterizzazione quantitativa del materiale nella tomografia computerizzata a raggi X spettrale

This doctoral thesis embarks on a comprehensive journey of exploring the potential of spectral X-ray imaging in medicine, employing advanced techniques and cutting-edge technologies to harness the full potential of X-ray interactions with matter. The study is divided into several chapters, each contributing to our understanding of how spectral imaging, particularly through photon counting detectors and synchrotron radiation X-ray setups, can revolutionize medical diagnostics and material characterization. The research begins by delving into the intricate physics of X-ray interactions, encompassing X-ray attenuation and phase shift in matter. It lays the foundation for the subsequent exploration of X-ray detection methodologies, encompassing photon counting detectors and addressing challenges like charge sharing and pulse pile-up. A central theme of this work is quantitative imaging, focusing on material decomposition as an intermediary process for computing material characteristics - material density and effective atomic number. These quantities are derived through a mathematical framework that encapsulates the connection between decomposed material maps and the maps representing density and effective atomic numbers. Innovative material decomposition techniques such as singular value material decomposition were addressed through a comprehensive theoretical framework. Careful evaluation of the concept of effective atomic number was performed by comparing the methods published in several papers. The exploration extends to spectral data acquisition techniques, spanning dual-energy imaging systems available on earlier-generation clinical CT scanners, multi-energy photon-counting CT scanners, and pre-clinical spectral imaging using synchrotron radiation CT systems, shedding light on the advantages and disadvantages of new technology. The photon-counting detectors as a state-of-the-art technology for clinical spectral imaging were addressed in the framework of a virtual imaging platform developed at Duke University. The work consisted of modeling spatial-energetic detector response and addressing non-idealities like charge sharing and pulse pile-up. The model was validated against real measurements and special attention was focused on the influence of these non-idealities on the accuracy of spectral information, and thus the correctness of quantitative information obtained from such datasets. Besides virtual investigation, the thesis highlights the potential of the first clinical photon-counting CT scanner through the comparative assessment with dual-energy CT, demonstrating the superiority of photon-counting CT in iodine quantification at lower radiation doses. The investigation extends to synchrotron spectral CT, with a specific focus on estimating the density and effective atomic number of adipose, fibro-glandular, and cancer tissue. Synchrotron breast CT imaging was carried out at the SYRMEP beamline of Elettra, an Italian synchrotron light source in Trieste, in the framework of SYRMA-3D (SYnchrotron Radiation for MAmmography) collaboration. This endeavor illuminates the potential to differentiate various breast tissues based on their quantitative characteristics and lays the groundwork for other various spectral synchrotron-based X-ray imaging setups.