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Superior material discrimination provided by photon counting detector (PCD) technology promises to transform X-ray CT into a functional and molecular imaging modality while maintaining its high spatial resolution, fast scanning times, and relatively low cost. Our group has developed pre-clinical photon-counting CT (PCCT) prototype systems and applied them, in combination with nanoparticle contrast agents, for cancer and cardiac imaging. This work aims to compare the PCCT imaging performance using a gallium arsenide (GaAs) and a cadmium telluride (CdTe) based PCD, both with 150- μm pixels and 4 energy thresholds. The two PCDs were integrated in the same PCCT system. Phantoms containing elemental solutions of Iodine, Gadolinium, Tantalum, Hafnium, Bismuth and Calcium were imaged with each detector to establish the spectral separation capabilities for PCCT. Moreover, combined dual detectors PCCT imaging was also tested. A joint iterative reconstruction followed by image-based material decomposition was used to provide material maps of different elements. The accuracy of the estimated concentrations within the material decompositions were compared. Our results have shown that GaAs-based PCCT imaging has an overall higher sensitivity (by ~15%) to Iodine than CdTe when using identical acquisition parameters. The CdTe imaging, has higher quantum efficiency at high keVs, supporting higher source kVps and energy threshold settings for imaging the K-edges of Bismuth or other high-Z NPs (such as Gold). Based on the average vial measurements, hybrid GaAs-CdTe PCCT decompositions have the most accurate decompositions for nearly all materials except for Bismuth. The combination of CdTe and GaAs PCDs into a dual source PCCT system will provide high sensitivity in separating multi-element contrast agents from intrinsic tissues.
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