A novel CT detector based on CMOS photodiodes has been developed. A detector module comprises two identical photosensor arrays mounted to a ceramic substrate. Each sensor has a matrix of 20 by 10 pixels. Pixels are 1 mm (channel direction) x 1.8 mm (slice) large and consist of a photodiode, charge integration unit and a sample
and hold stage. An automated switching between a low and a high sensitivity mode allows for a dynamic range of 17 bits. The integrated signals are read out, transferred to a printed circuit board (at a rate of 2463 Hz per pixel) and here converted into a digital data stream. The structured cadmium tungstate scintillator features lead stripes between pixels to reduce x-ray crosstalk and to shield the underlying in-pixel electronics. During assembling care was taken to ensure that the lead stripes of the scintillator entirely cover the pixel electronics underneath. Several prototype modules have been assembled and their performance concerning linearity, noise, crosstalk, and temperature dependence has been evaluated.
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