Optimal architecture of CdZnTe detectors for photon counting, multispectral medical x-ray imaging: Comparison between simulation and experiment

In this work, we combine a number of pixellated, high quality CdZnTe crystals of different configurations with a unique, fast electronic readout system with dynamic energy binning capabilities to develop a novel detection system capable of photon-counting, multispectral medical x-ray imaging. This technique offers significant advantages over conventional medical x-ray imaging by providing improved image quality through a reduction in beam hardening artefacts and better scatter rejection; enhanced soft tissue contrast, improving on current dual energy techniques by taking full advantage of the variation in mass attenuation coefficients of different tissues; in the development of K-edge imaging, identifying different high-Z contrast agents in a single scan; and in a significant reduction in radiation dose to the patient. This state-of-the-art readout system has eight dynamic energy bins, controlled by variable threshold voltages on comparator circuits with 16-bit counters. Using a novel technique of interchangeable CdZnTe dies, a wide range of detector configurations have been tested, providing the most complete experimental description of charge transfer effects within CdZnTe crystals. Pixellated CdZnTe crystals of thicknesses ranging between 1 and 3 mm and pixel sizes ranging between 100 and 400μm have been rigorously tested to determine the energy response, linearity, and stability of each crystal with an investigation into polarisation and charge sharing effects in order to provide a comprehensive comparison between simulation and experimental. Using the most advanced photoncounting, dynamic energy binning electronic readout system to date has allowed us to determine the optimum configuration for the electronic readout for medical x-ray imaging, providing essential information regarding the number of energy bins required for task specific medical imaging.