In vivo imaging demonstration using a two-dimensional SiPM-based photon-counting CT system: Preliminary results

Photon-counting computed tomography (PC-CT) is a next-generation imaging technology that enables material discrimination and quantitative evaluation through energy-resolved photon detection. In our previous study, we developed a one-dimensional (1D) PC-CT system consisting of silicon photomultipliers (SiPMs; multipixel photon counters, MPPCs) coupled with yttrium-gadolinium-aluminum-gallium garnet (YGAG) scintillators in a matched 1 × 64 pixel configuration, and successfully demonstrated material discrimination and quantitative concentration estimation. In this study, as a step toward dynamic imaging, we developed a two-dimensional (2D) PC-CT system employing a 1024-channel detector array composed of 16 × 64 pixels, in which MPPCs are coupled with YGAG scintillators. Signals from the MPPCs are read out and processed using multiple custom-developed large-scale integration (LSI) circuits. We evaluated the spectroscopic and counting performance of the system and found an average energy resolution of 41 . 2 ± 1 . 6 % (FWHM at 59.5 keV) over the 1024 channels, as well as a maximum count-rate tolerance of 6.3 MHz, both of which are comparable to those of the 1D system. To demonstrate the applicability of the system to dynamic imaging, preliminary in vivo imaging experiments were performed using a mouse administered with a gadolinium-based contrast agent. As a result, the total imaging speed was increased by approximately a factor of ten compared to that of the 1D system. Furthermore, the in vivo distribution of gadolinium was successfully visualized, indicating that the developed 2D PC-CT system is promising for future dynamic clinical imaging applications.