Development of active matrix flat panel imagers incorporating thin layers of polycrystalline HgI₂for mammographic x-ray imaging

Abstract

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 signal-to-noise ratio by virtue of its low effective work function (WEFF). 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 WEFF values of ~19 eV), low dark current (<0.1 pA/mm2) and good spatial resolution, largely limited by the size of the pixel pitch, were observed. For one prototype, a detective quantum efficiency of ~70% was observed at an x-ray exposure of ~0.5 mR at 26 kVp.

Characterization of polycrystalline lead oxide for application in direct conversion X-ray detectors

“…The later can be improved by developing a PbO blocking structure, as it was successfully done for a-Se 16 . However, HgI 2 layers are toxic in the sense that they chemically react with imaging array electronics, thus creating additional technological challenges 39 , 40 . Currently, the major competitors of PbO seems to be perovskite photoconductors, for example methylammonium lead iodide (CH 3 NH 3 PbI 3 ).…”

Bent HgI2 Molecules in the Melt and Sulfide Glasses: Implications for Nonlinear Optics

“…Mercury (II) iodide HgI2 has been extensively studied over the last few decades owing to multiple applications in room-temperature X-ray and gamma-ray detection; 5,6 it is particularly useful for flat panel medical imaging technologies. 7,8 HgI2 also has promising optical properties 9,10 and creates a vivid interest in a fundamental field. [11][12][13] The mercury (II) iodide vapor consists of linear HgI2 triatomic molecules confirmed by gas-phase electron diffraction 14,15 and Raman spectroscopy.…”

Charge transport in pure and stabilized amorphous selenium: re-examination of the density of states distribution in the mobility gap and the role of defects

“…This imaging modality needs photoconductors that have a higher atomic number (Z). Higher Z semiconductors such as CdTe, CdZnTe, HgI 2 , PbI 2 , PbO have shown good potential for applications in direct conversion imaging with favorable electrical properties; see, for example, references [16][17][18][19][20][21][22][23][24] for a selection of potential high-Z semiconductors, some of which were reported in this journal.…”