Custom column readout circuitry to extend the dynamic range of a-Si:H current mediated pixel amplifiers for large area diagnostic X-ray imaging applications

In real-time X-ray fluoroscopy, the patient is continuously exposed to radiation, hence requiring a reduced X-ray dose which results in small input signals to the digital imaging pixel electronics. Conventional switch based amorphous silicon imagers result in poor signal-to-noise ratios (SNR) at low fluoroscopic exposure levels due to noise added by pixel readout electronics. In contrast, amorphous silicon amplified pixels have been reported to give a good SNR for fluoroscopy but their output becomes non-linear for higher doses, limiting their use to low exposure X-ray imaging applications. In this research, we present modifications to column readout amplifier electronics that can extend the dynamic range of an amplified pixel. The larger dynamic range is of particular relevance for amplified pixels used in dual-mode imagers that can switch instantaneously between fluoroscopy and higher contrast chest radiography imaging modes.