An investigation into the temporal stability of CdTe-based photon counting detectors during spectral micro-CT acquisitions

Spectroscopic micro-computed tomography (CT) using photon counting detectors is a technology that promises to deliver material-specific images in pre-clinical research while suppressing noise related to dark current. Inherent to such applications is the need for a high spatial resolution, which can only be achieved with small focal spot sizes in the micrometre 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. During the past years, the Medipix3RX detector has become a popular platform for research into low-flux and multi-energy CT, as it hosts a number of elaborate features that may serve as an inspiration for future systems when studied carefully. In this contribution, we illustrate our findings on how to reduce image artefacts in CT reconstructions using such a detector with a cadmium telluride sensor. We find that maintaining a constant temperature is a prerequisite to guarantee energy threshold stability. More importantly, we identify transient sensor leakage currents as a significant source to artefact formation. We demonstrate an improvement in image quality when allowing the chip to compensate for abnormally high leakge currents. The reduction of spectral resolution reported earlier for such settings is found to have no detrimental effect on material decomposition. Quite the contrary, the improved handling of transient leakage currents allows to even increase contrast-to-noise ratios in material decomposed images due to a reduced artefact level.