Characterization of noise and efficiency of the Pixirad-1/Pixie-III CdTe X-ray imaging detector

Thanks to their high detection efficiency and low intrinsic noise, direct conversion X-ray Photon Counting Detectors (XPCDs) are particularly suitable for low dose imaging applications such as mammography. The photon counting technology can implement also two or more acquisition thresholds to perform single-shot spectral imaging with one polychromatic source. However, XPCDs with thick high Z crystal sensor and small pixel size are affected by the charge sharing effect. This issue can induce multiple counts from a single interaction reducing both spectral and spatial resolutions. In a pure counting mode, multiple counts from charge sharing can be partially or totally removed by increasing the acquisition threshold at the cost of a loss of efficiency. Thus, the performances of XPCDs can be threshold-dependent. New generation XPCDs implement solutions to cope with charge sharing issue. If the charge sharing is properly corrected, no multiple counts are recorded and the performances (detection efficiency, spectral and spatial resolutions) of the acquisition system are expected to be independent from the acquisition threshold. This work presents a study of a Pixirad-1 detection system based on a CdTe Schottky sensor and PIXIE-III readout system. This chip can be configured in three different operation modes, two of which implement solutions to remove multiple counts. Using monochromatic radiation, the performances of these different operation modes have been compared trough a measure of the integral spectra and the Signal to Noise Ratio (SNR) as function of the acquisition threshold.