High-resolution CMOS imaging detector

A 2.5 cm by 5 cm, 512 by 1024 pixel CMOS photodiode array detector designed specifically for digital radiography will be described. All necessary scanning and readout circuitry is integrated within the detector. The small pixel spacing of 48 micrometers allows the imager to easily achieve the 10 lp/mm resolution required for the targeted interventional mammography application. Direct coupling to the scintillator and a pixel fill factor of more than 80% leads to high DQE over a large range of exposure values. The detector exhibits very low dark current of about 30 pA/cm2 at room temperature, which allows for low-noise operation and long integration times. Read noise of less than 200 electrons rms and a saturation level of 2.8 X 106 electrons combine for a large dynamic range greater than 80 dB. The conversion gain of the detector is 0.5 (mu) V/electron. Combined with a Gd2O2S scintillator, the imager achieves up to 25% MTF at 10 lp/mm and a DC detective quantum efficiency of 50%. The detector design is optimized for x-ray energies between 10 kV and 50 kV, but can be retrofitted with different scintillator screens to cover a large range of imaging applications up to 160 kV.

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