Overcoming detector limitations of x-ray photon counting for preclinical microcomputed tomography

Spectral computed tomography (CT) using photon counting detectors (PCDs) can provide accurate tissue composition measurements by utilizing the energy dependence of x-ray attenuation in different materials. PCDs are especially suited for K-edge imaging, revealing the spatial distribution of select imaging probes through quantitative material decomposition. We report on a prototype spectral micro-CT system with a CZT-based PCD (DxRay, Inc.) that has 16 x 16 pixels of 0.5 x 0.5 mm(2), a thickness of 3 mm, and four energy thresholds. Due to the PCD's limited size (8 x 8 mm(2)), our system uses a translate-rotate projection acquisition strategy to cover a field of view relevant for preclinical imaging (similar to 4.5 cm). Projection corrections were implemented to minimize artifacts associated with dead pixels and projection stitching. A sophisticated iterative algorithm was used to reconstruct both phantom and ex vivo mouse data. To achieve preclinically relevant spatial resolution, we trained a convolutional neural network to perform pan-sharpening between low-resolution PCD data (247-mu m voxels) and high-resolution energy-integrating detector data (82-mu m voxels), recovering a highresolution estimate of the spectral contrast suitable for material decomposition. Long-term, preclinical spectral CT systems such as ours could serve in the developing field of theranostics (therapy and diagnostics) for cancer research. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)