Amorphous selenium (a-Se) has been incorporated successfully in direct conversion flat panel x-ray detectors, and has
demonstrated superior image quality in screening mammography and digital breast tomosynthesis (DBT) under energy
integration mode. The present work explores the potential of a-Se for photon counting detectors in DBT. We investigated
major factors contributing to the variation in the charge collected by a pixel upon absorption of each x-ray photon. These
factors included x-ray photon interaction, detector geometry, charge transport, and the pulse shaping and noise properties
of the photon counting readout circuit. Experimental measurements were performed on a linear array test structure
constructed by evaporating an a-Se layer onto an array of 100 μm pitch strip electrodes, which are connected to a 32
channel low noise photon counting integrated circuit. The measured pulse height spectrum (PHS) under polychromatic xray
exposure was interpreted quantitatively using the factors identified. Based on the understanding of a-Se photon
counting performance, design parameters were proposed for a 2D detector with high quantum efficiency and count rate
that could meet the requirements of photon counting detector for DBT.
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