Dynamic Properties of Flat-Panel X-Ray Image Sensors With Mercury Iodide Photoconductors Undergoing Repeated X-Ray Irradiation

A screen-printed mercury iodide (HgI 2 ) photoconductor for digital tomosynthesis exhibits considerably reduced signals when subjected to consecutive exposures to X-ray irradiation. This behavior accounts for the trapping of charges generated on previous X-ray shots near the HgI 2 /electrode interface. These trapped charges create the conditions that deter subsequent charges generated by the next X-ray shot from traveling from the photoconductor into the electrode. Such conditions can be improved significantly by switching the bias polarity of the photoconductor with an illuminating light under the image sensor. In addition, the signal-to-noise ratio (SNR) is optimum when the duration of the illuminating light is 1 s longer than the applied time of the positive bias. Increases in the bias switching/lighting combination time for obtaining the best SNR are required with increasing amounts of incident X-ray exposure. Such results obtained from making adjustments in the technique for using screen-printed HgI 2 photoconductors for digital tomosynthesis indicate promising results for improving the diagnostic accuracy of this digital imaging method for breast cancer screening while mitigating patients' X-ray exposure.