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A cost-effective digital radiographic system with a large field-of-view (FOV) of 17 17 has been developed. The cascaded imaging system mainly consists of three parts: 1) a phosphor screen to convert incident X-rays into visible photons; 2) a matrix of 8 8 array of lens assembly to efficiently collect visible photons emitted by the phosphor screen; and 3) 8 8 complementary metal-oxide-semiconductor (CMOS) image sensors, aligned to the corresponding lens assembly. Although low in cost due to economical CMOS image sensors, the overall performance features are comparable with other commercial digital radiographic systems. From the analysis of signal and noise propagation, the system is not an "X-ray quantum-limited" system, rather the system has secondary quantum sink at the light collecting stage. The system resolution is about 2 line pairs per millimeter from both of measured from X-ray images of a line-pair test pattern and the calculation of the modulation-transfer function. Detailed experimental and theoretical analysis of performance will be discussed.Index Terms-Complementary metal-oxide-semiconductor (CMOS), digital radiography (DR), parallel-hardware architecture, X-ray imaging.

The gas electron multiplier (GEM), placed in the drift volume of a conventional gas detector, is a conceptually simple device for producing a large gas gain by concentrating the drift electric field over a very short distance to the point that electron avalanching occurs. This device consists of a thin insulating foil of several tens of μm in thickness, covered on each side with a thin metal layer, with tiny holes, usually 100 μm or less in diameter, and with a spacing of 100-200 μm through the entire foil, perforated by using chemical etching or high-powered laser beam technique. In this study, we have investigated its operating properties with various experimental conditions and demonstrated the possibility of using this device as a digital X-ray imaging sensor, by acquiring X-ray images based upon the scintillation lights of the GEM with a standard CCD camera.