Optimizing CdTe detectors and ASIC readouts for high-flux x-ray imaging

Abstract

Developments in room temperature cadmium telluride (CdTe) based solid state imaging arrays for energy-resolved photon-counting in medical x-ray imaging are discussed. A number of x-ray imaging applications can benefit from these developments including mammography, radiography, and computed tomography (CT). Energy-resolved photon-counting can provide reduced dose through optimal energy weighting, compositional analysis through multiple basis function material decomposition, and contrast enhancement through spectroscopic x-ray imaging of metal nanoparticles. Extremely high flux can occur in x-ray imaging and energy integrating detectors have been conventionally used. To achieve the benefits of energy resolved photon counting, imaging arrays with a large count rate range and good detection efficiency are required. Compound semiconductor radiation detectors with pixellated anode arrays electrically connected to application specific integrated circuits (ASICs) can provide fast, efficient, low-noise performance with adequate energy resolution however this can only be achieved with a careful optimization of the CdTe sensors and ASICs together. We have designed and constructed CdTe imaging arrays, 3 mm thick with a grid of electrical contacts inter-connected to a multi-channel channel ASICs. Arrays with a pixel pitch of 0.5 mm have achieved a counting range up to 20 million counts per second per square mm. Additionally, ASICs with a two dimensional array of pads has been fabricated and tested by connecting the inputs to 1 mm pitch CdTe sensors demonstrating 7 keV full width at half maximum energy resolution across a dynamic range of 30 keV to 140 keV for clinical CT.