Development of a digital gamma imaging system based upon the CMOS imager coupled with a CdTe photoconductor for nondestructive testings

As a continuation of our digital radiographic sensor R&D, we have developed a digital gamma imaging system based upon the CMOS imager coupled with a cadmium-telluride (CdTe) photoconductor for our ongoing application of nondestructive testings. The imaging system consists of a commercially-available CMOS readout array with a 100 times 100 mum² pixel size and a 5.4 times 151.0 mm² active area, coupled with a 750-mum-thick CdTe photoconductor, and a collimated selenium (⁷⁵Se) gamma source with an about 62.8 Ci activity and a physical size of 3.0 mm in diameter. In this study, we, for the first time, succeeded in obtaining useful gamma images with the ⁷⁵Se source and evaluated the imaging performance of the system in terms of the line spread function (LSF), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). For comparison, we also evaluated the image quality with a microfocus X-ray source with an about 5 mum focal spot at a given test condition of 90 kV_p and 100 muA.