X-Ray Imaging of Anticancer Drugs and a Platinum-Iodine Mixture Encapsulated in Liposomes Using SiPM-Based Photon-Counting CT

X-ray computed tomography (CT) is a non-destructive imaging technique used to visualize the internal structures of objects across various fields, including medicine. Among recent advancements, photon-counting CT (PC-CT) system has emerged as a promising technology that detects X-rays on a photon-by-photon basis, enabling energy-resolved imaging for material identification and quantitative density assessment. In this study, we employed our established PC-CT system, which integrates yttrium–gadolinium–aluminum–garnet doped with cerium (YGAG:Ce) scintillators combined with silicon photomultipliers (SiPMs) to evaluate the distribution of liposomeen-capsulated anti-cancer drugs: carboplatin, used in ovarian cancer treatment, and oxaliplatin, used in colorectal cancer treatment. Furthermore, we assessed the material discrimination capability for liposomes containing both platinum and iodine. The experimental results demonstrated that the low concentrations of platinum, originating from the platinum-based drugs carboplatin and oxaliplatin, encapsulated in liposomes, could be estimated with high accuracy within the experimental uncertainties. For concentration estimation, we combined CT images acquired at multiple energy ranges, taking into account the transmitted X-ray energy spectrum; the mass attenuation coefficients of relevant materials, including the intrinsic CT values of the liposomes; and the detector response, such as the scintillator detection efficiency and the energy resolution. Additionally, for liposomes containing both platinum and iodine, compensation for pulse pileup effects significantly improved the estimation of CT values for multi-energy bands at high X-ray flux rates, thereby facilitating to material discrimination and enhancing the accuracy of concentration estimation in objects containing multiple substances. This study demonstrates the utility of PC-CT in visualizing the distribution of anti-cancer drugs and discriminating between materials, thereby contributing to the development of innovative diagnostic and therapeutic methods in cancer treatment utilizing drug delivery systems.