Estimation of contrast agents using a 2-dimensional photon counting CT detector combined with MPPC and YGAG scintillator array

Abstract

The potential of photon-counting (PC) detectors in medical CT imaging is supported by their ability to count individual photons and measure their energy simultaneously, enabling multi-energy imaging with adjustable energy settings that enhance diagnostic accuracy. Contrast-enhanced CT imaging further improves diagnostic performance by allowing differentiation based on the distinct energy-dependent attenuation profiles of each contrast agent. The development of PCCT, consisting of the multi-pixel photon counter (MPPC) array and the yttrium-gadolinium-aluminum-gallium garnet (YGAG) scintillator array, has been expanded from a 1-dimensional to a 2-dimensional detector, thereby reducing the imaging time and enhancing temporal imaging resolution. The 2-dimensional PCCT uses a 256-channel pixel array (with 1 × 1 mm${}^2$ for each pixel size), configured as 16 × 16 pixels. Signals from this array are processed by four large-scale integrated circuit boards, each handling 64 channels with six energy thresholds and capable of ultra-fast analog and digital signal processing exceeding 10 MHz per channel. CT imaging was performed on both non-mixture and mixture samples containing iodine and gadolinium using the 2-dimensional PCCT system. Concentration estimation from multiple-energy CT image data was performed, and a 3-dimensional concentration mapping for both non-mixture and mixture samples was achieved with a concentration accuracy of 0.2–1.8 mg/mL, demonstrating the capability of material discrimination in mixture sample. Furthermore, a preliminary demonstration of dynamical imaging using the 2-dimensional PCCT system was conducted. The temporal changes in quantitative data from multiple time-point images were successfully obtained, demonstrating the potential of the system for future dynamic clinical imaging applications, such as assessing blood flow and vessel dynamics.