Development of active matrix flat panel imagers incorporating thin layers of polycrystalline HgI2 for mammographic x-ray imaging

Active matrix flat-panel imagers (AMFPIs) offer many advantages and have become ubiquitous across a wide variety of medical x-ray imaging applications. However, for mammography, the imaging performance of conventional AMFPIs incorporating CsI:Tl scintillators or a-Se photoconductors is limited by their relatively modest signal-to-noise ratio (SNR), particularly at low x-ray exposures or high spatial resolution. One strategy for overcoming this limitation involves the use of a high gain photoconductor such as mercuric iodide (HgI2) which has the potential to improve the SNR by virtue of its low effective work function (W-EFF). In this study, the performance of direct-detection AMFPI prototypes employing relatively thin layers of polycrystalline HgI2 operated under mammographic irradiation conditions over a range of 0.5 to 16.0 mR is presented. High x-ray sensitivity (corresponding to W-EFF values of similar to 19 eV), low dark current (<0.1 pA mm(-2)) and good spatial resolution, largely limited by the size of the pixel pitch, were observed. For one prototype, a detective quantum efficiency of similar to 70% was observed at an x-ray exposure of similar to 0.5 mR at 26 kVp.