Energy-resolved photon-counting x-ray imaging arrays for clinical K-edge CT

Abstract

We have fabricated a fast energy-resolved photon-counting x-ray imaging array using pixellated cadmium telluride (CdTe) semiconductor sensors and have achieved an output count rate (OCR) exceeding 20 million counts per second per square mm (Mcps/mm2) measured with a clinical computed tomography (CT) x-ray source. We have also fabricated a fast application specific integrated circuit (ASIC) with a two dimensional (2D) array of inputs for readout from pixellated direct-conversion CdTe or cadmium zinc telluride (CdZnTe) sensors. The new 2D ASICs have four energy bins with a linear energy response across the entire dynamic range for clinical CT, which is between 30 keV and 140 keV. We have measured several important performance parameters including an energy resolution of 8 keV FWHM across the entire dynamic range and a noise floor less than 23 keV by connecting the 2D ASIC to a CdTe sensor. The uniform energy resolution over the entire dynamic range is an indication of good charge collection from the direct conversion sensors. The energy resolution is maintained at high flux over long varying exposure to x-rays indicating polarization free performance from the sensors. Our results demonstrate fast output count rates from a clinical CT x-ray source, with good energy resolution and a low noise floor. The sensors and ASICs are designed to fit into existing clinical CT systems.