Analysis of the detective quantum efficiency of coupling a CCD to a scintillating phosphor for x-ray microtomographic imaging

摘要

Abstract: We are developing an x-ray microtomographic imaging system ($mu@CT) for imaging small objects at very high (approximately 25 $mu@m) spatial resolution. The detector for this system consists of a CCD array coupled to a phosphor screen through a fiber-optic faceplate. For the purposes of signal and noise analysis, this system is modeled as a multi-stage cascaded imaging system consisting of: (a) conversion of x-ray quanta to optical quanta in the phosphor; (b) collection and transfer of optical quanta from the phosphor to the CCD; and (c) detection of optical quanta by the CCD. We use the model of Rabbani et al. for cascaded systems to theoretically calculate the detective quantum efficiency (DQE) as a function of spatial frequency. We have developed the theoretical basis of a spatial-frequency dependent nomogram in terms of the system DQE. This approach is used to identify any sources of image degradation, and to make optimal design decisions of system parameters such as optical gains or numerical apertures. Using this approach, we show that the spreading of optical photons in the phosphor screen is the most significant factor degrading the MTF.!18