Multi-energy in-vivo imaging of multiple contrast agents in a mouse using MPPC-based photon-counting CT

Contrast -enhanced computed tomography (CT) is an indispensable technique in modern diagnostic medicine because it not only allows non-destructive, three-dimensional observation of the inside of the body but also provides images that highlight lesions. Recent developments in photon -counting (PC) CT systems have enabled contrast -enhanced CT scanning and quantitative evaluations, such as material discrimination and concentration estimation of contrast agents, using X-ray energy information. We established a PC -CT system that combines fast scintillators and multipixel photon counters (MPPCs) and demonstrated its performance. In this paper, we report the imaging performance of a PC -CT system using a mixture of contrast agents containing gadolinium and iodine. We performed CT imaging of a static phantom containing a mixture of the two contrast agents. The concentration of each contrast agent from the CT images in multiple energy bands were estimated. We succeeded in obtaining the concentration distributions for each contrast agent and verified the possibility of discriminating between two substances with different atomic numbers. In addition, the same procedures and analytical methods used for the static phantom were applied to the in vivo imaging of a mouse, in which gadolinium- and iodine -containing contrast agents were injected at different time intervals. We also succeeded in discriminating between the two contrast agents in vivo, making it possible to provide new imaging diagnostics such as the determination of necrotic tissues and normal blood vessels. Furthermore, we succeeded in creating three-dimensional concentration maps of gadolinium and iodine in a mouse, demonstrating the great potential of MPPC-based PC -CT for future clinical applications.