Development and evaluation of a digital radiographic system based on CMOS image sensor

A cost-effective digital radiographic system with a large field-of-view (FOV) of 17"/spl times/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/spl times/8 array of lens assembly to efficiently collect visible photons emitted by the phosphor screen; and (3) 8/spl times/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 are discussed.