Reducing the formation of image artifacts during spectroscopic micro-CT acquisitions

Spectroscopic micro-computed tomography using photon counting detectors is a technology that promises to deliver material-specific images in pre-clinical research. Inherent to such applications is the need for a high spatial resolution, which can only be achieved with small focal spot sizes in the micrometer range. This limits the achievable x-ray fluxes and implies long acquisitions easily exceeding one hour, during which it is paramount to maintain a constant detector response. Given that photon-counting detectors are delicate systems, with each pixel hosting advanced analog and digital circuitry, this can represent a challenging task. In this contribution, we illustrate our findings on how to reduce image artifacts in computed tomography reconstructions under these conditions, using a Medipix3RX detector featuring a cadmium telluride sensor. We find that maintaining a constant temperature is a prerequisite to guarantee energy threshold stability. More importantly, we identify varying sensor leakage currents as a significant source to artifact formation. We show that these leakage currents can render the corresponding images unusable if the ambient temperature fluctuates, as caused by an air conditioning, for example. We conclude with demonstrating the necessity of an adjustable leakage current compensation.