Large area photon counting X-ray imaging arrays for clinical dual-energy applications

We report on the development of fast photon counting X-ray imaging arrays for dual-energy clinical applications. In order to provide the arrays with adequate performance for clinical dual-energy applications, we have designed and fabricated a novel four threshold application specific integrated circuit (ASIC) for single photon counting readout from pixellated direct-conversion CdTe sensors. The ASIC readout and CdTe photon counting detectors are integrated into modules so that the modules can be tiled in one dimension for the fabrication of large area arrays. Recently we have developed novel CdTe arrays which significantly reduce the noise floor allowing for low energy clinical imaging applications. We report on a characterization study of a prototype large area detector which can be used for the generation of two or three dimensional dual energy X-ray absorptiometry (DEXA) images. The prototype CdTe array has 256 pixels with about a 1 mm pitch. We have measured several important detector parameters including the maximum output count rate, energy resolution, and noise performance. A maximum output rate of 0.6 million counts per second per pixel has been obtained with a low noise floor below 7 keV and an energy resolution of 6% at 60 keV. All detector noise counts are less that 7 keV which is sufficiently low for clinical DEXA. Our results demonstrate noise and spectral characteristics that make these X-ray imaging arrays ideally suited for clinical DEXA.