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Spectral CT using photon counting x-ray detectors (PCXDs) can provide accurate tissue composition measurements by utilizing the energy dependence of x-ray attenuation in different materials. PCXDs are especially suited for imaging Kedge contrast agents, revealing the spatial distribution of select imaging probes through quantitative material decomposition. To further advance the field, there is a clear and continuing need to develop PCXD hardware and software as part of a new generation of spectral CT imaging systems. Our group specializes in the development of preclinical microCT systems and of novel imaging probes based on K-edge materials. Toward this goal, we have now developed a prototype spectral micro-CT system with a PCXD produced by DxRay. This CZT-based PCXD has 16x16 pixels, each with a size of 0.5 x 0.5 mm, a thickness of 3 mm, and 4 configurable energy thresholds. The detector is thus only 8 mm x 8 mm in size. Due to the limited size of this detector tile, we have implemented a translate-rotate micro-CT system (i.e. a 2nd generation scanner). In this paper we summarize considerable efforts which went into compensating for dead pixels and for pixels with non-linear responses to prevent artifacts in the CT reconstruction results. We also present spectral response measurements for the detector and the results of both phantom and animal experiments with iodine- and gold-based contrast agents. The results confirm our ability to sample and reconstruct tomographic images, but also show that the PCXD prototype has limitations in imaging iodine.
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