System considerations in CCD-based x-ray imaging for digital chest radiography and digital mammography.

System modeling is used to investigate the effect of various system parameters on the image quality in CCD-based x-ray imaging systems. The systems considered consist of a typical phosphor-based scintillating screen coupled to a CCD through lens or fiberoptic taper. Two applications, chest radiography and mammography, are analyzed. For each application typical system characteristics and operating conditions are used to determine the detective quantum efficiency (DQE) as a function of spatial frequency, optical collection efficiency, optical demagnification factor, and electronic noise. The DQE is modeled by extending the analysis for storage phosphor systems. The calculations are done for typical exposure conditions (0.25 mR for chest and 10.0 mR for mammography); however, the exposure effects are also discussed. It was found that a reasonable DQE can be obtained for both applications through each coupling approach; however, the demagnification requirements and electronic noise limitations are more stringent for the digital mammography application.